Evolution and endemism in argyranthemum : Web ex Schultz Bip. (Compositae: Anthemideae)

              BOTÁNICA MACARONESICA 1 (1976)
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
Webb ex Schultz Bip.(Compositae: Anthemideae).
by C. J. HUMPHRIES
Dept. of Botany, British Museum (Natural History) London SW7 5 BD.
RESUMEN
C. J. Humphries: Evolución y Endetnismo en Argyranthemum Webb ex Schultz Bip. (Compositae:
Anthemideae).
1. El género Argyranthemum (Compositae: Anthemideae) está centralizado en las Islas
Canarias, en donde 18 de las 22 especies se encuentran en 4 de las 5 zonas principales de
vegetación. Otras 3 especies se presentan en el archipiélago de Madeira y una endémica en
Las Islas Salvajes.
2. El género, es probablemente de origen Terciario, presentando un ejemplo de radiación
adaptativa monofilética. Con respecto a la morfología los caracteres más adaptativos incluido
lanosidad, hábito, forma y anatomía de la hoja y tamaño de la flor. En un extremo se en­cuentran
con forma densa, arbustos muy lignificados perennes con amplia superficie de
hojas y un largo capítulo, mientras que en el otro extremo se encuentran especies ligeras,
poco ramificadas con ciclo de vida reducido, ligeramente leñosas y hojas muy divididas. El
género puede ser dividido en 5 secciones discretas basándose en la morfología de la cipsela.
3. La distribución de las 5 secciones se correlacionan estrechamente con las zonas prin­cipales
de vegetación y son así consideradas como representantes de viejas divergencias. Espe­cies
de las secciones Sphenismelia y Stigmatotheca probablemente poseen más atributos
morfológicos antiguos que las especies de las otras secciones ecogeográficas y paleogeográficas.
4. Cada especie se compone de poblaciones aisladas morfológicamente pequeñas pero
genéticamente amplias procurando una distribución «Rassenkreislehre».
5. La evolución ha sido un proceso gradual (todas las especies son diploides) por una
vigorosa selección natural de los genotipos adaptables en gradientes ecológicos escalonados.
El aislamiento entre las diferentes especies ha sido enteramente influenciado por fac­tores
extrínsicos ecológicos y posiblemente geográficos. El aislamiento genético se ha origi­nado
sólo por la acumulación de genes disarmónicos y han retardado una amplia vía re­basando
una divergencia morfológica y fisiológica.
6. Cada población tiene una clara ventaja selectiva en los habitats en que se encuentra.
Los híbridos se han formado sólo en las áreas de alteración masiva a pesar de la evidencia
de que existe una considerable transferencia de genes entre las poblaciones adyacentes.
CONTENTS
Introduction 26
Adaptive Radiation in the Macaronesian Islands 26
25
C.J. HUMPHRIES
Taxonomic Position of Argyranthemum 27
Geography of the Macaronesian Islands 27
Ecological Diversity in the Macaronesian Islands 28
Taxonomy and Adaptive Trends in Argyranthemum 34
Macaronesian Palaeogeography 39
Palaeogeography and Distribution in Argyranthemum 40
Cytology 41
Artificial Hybrids and crossing relationships 41
Natural Hybridisation 44
Discussion: Patterns of Evolution 46
Summary 48
INTRODUCTION
Of the 2500 species of flowering plants, which occur in the Macaronesian Islands,
the Azores, Madeira, the Salvage Islands, the Canary Islands and the Cape Verde
Islands some 600 species constitute the dominant endemic element (Bramwell, 1972;
Sunding 1973). As pointed out by Bramwell (1972) the Canary Island endemics, and
indeed the Macaronesian endemics as a whole fall into three main categories; the relicts
or palaeoendemics, which are taxa surviving in a remnant of their former territory and
have no easily identifiable relatives elsewhere, the neoendemics which have arisen by
evolution in the Macaronesian Islands from various easily identifiable continental
elements and the active epibiotics which are neoendemics derived from a palaeoendemic
stock. Active epibiotics are morphologically and ecologically diverse, with representative
taxa occurring in most principal habitats in a large number of the islands. Argyran­themum
Webb ex Sch. Bip. is ene such genus, consisting of twenty - two species
distributed in 4 of the 5 major vegetation zones of the Canary Islands, the Salvage
Islands and the islands of the Madeiran archipelago (Humphries 1973; 1975 (a)).
In this paper an attempt has been made to examine why so many species of Argyran­themum
occur in such a small total surface área and to give some idea of their evolu-tionary
history in relation to ecology, geography and palaeogeography.
ADAPTIVE RADIATION IN THE MACARONESIAN ISLANDS
The evolution of active epibiotics from the palaeoendemic flora has proceeded
mainly by a process of adaptive allopatric divergence in response to the wide range
of habitats and the isolated island condition characteristic of the Macaronesian región.
Lems, (1960) and Bramwell (1972 (a) and (b)) have demonstrated various morpholo-gical
trends associated with adaptive radiation in different endemic sections of Maca­ronesian
genera such as Aeonium Webb & Berth. (Crassulaceae), Sonchus L. (Compo-sitae)
and Echium L. (Boraginaceae), suggesting that 'diversification of form in
response to [selection] pressures, is a positive process where genetical response to
the stimulus of the environment is the main factor'. Also, as an explanation for
apparently random morphological variation in vicariant species of different localities,
but in similar ecological habitats, Bramwell (1972) invokes genetic drift and weak
selection as an explanation for divergence.
Evidence accumulated from ecological, morphological, cytological and hybridi­sation
studies in Argyranthemum suggests that powerful differential selection in
26
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
steep ecological gradients with extremely narrow ecotones, i. e. external isolating
mechanisms, has created an allopatric speciation pattern which accounts equally for
divergence in widely different species as well as closely related vicariants. Comparison
of distributions with palaeogeographical data suggests also that adaptive phenotypes
can be directly equated with known geological events and provides partial dated
evidence for the phylogenetic history of the genus.
THE TAXONOMic POSITION OF ArgyrarUhemum
Within the Anthemideae, Argyranthemum is one of the most distinctive Oíd World
genera of the Chrysanthemuin L. complex, closely allied to the Mediterranean sister
group annuals of Chrysanthemum L. sensu stricto and Heteranthemis Schott. Morpholo-gically
these three genera can be distinguished from all others in the Chrysanthemum
complex on the basis of their heteromorphic v. homomorphic cypselas and unmodified
pericarp anatomy (Humphries, 1973). In turn all species of Argyranthemum can be
distinguished from Chrysanthemum and Heteranthemis by their perennial habit,
their unique bi - sporic embryo sac development (Harling, 1951; Borgen, 1972), and
their flavonoid profile (Greger, 1969; Humphries, 1973).
The most closely related species of the sister group is Chrysanthemum carinatum
Schousb., a distinctive North African endemic from the south Atlantic coast of
Morocco. With Heteranthemis viscidohirta Schott, C carinatum shares a similar
cypsela morphology to the distinctive Canary Island laurel forest species Argyran­themum
broussonetii (Pers.) Humphries, but is easily characterised by its annual habit,
the tricoloured ray florets (yellow, white and maroon) the deep red corolla lobes of
the disc florets, and the tetra - sporic embryo sac development. A. broussonetii has,
together with the generic characters already mentioned, white ligules and yellow
corolla lobes on the disc florets. The red pigmentation of the ligules and disc corolla
lobes in C carinatum is found also in another species of Argyranthemum section
Sphenismelia; the Madeiran coastal endemic, A. haemotomma (Lowe) Lowe. It
seems, therefore, that Argyranthemum has a morphological and phytogeographical
link with the Mediterranean annual species of Chrysanthemum, this link being between
the predominantly laurel forest and halophyte species of Macaronesia and a coastal
species from the African continent.
This is interesting since Schmid (1955), considers Argyranthemum to have had
its origins in the Mediterranean flora and possibly associated with the Miocene Laurel
forest elements of Europe. These have been extinct since the Pliocene and now only
exist as relictual fragments in the Western Canary Islands and Madeira.
GEOGRAPHY OF THE MACARONESIAN ISLANDS
The Cañarían archipelago consists of seven major islands and five minor islets
(Fig. 1) lying to the west of the Spanish Sahara and bordering the oval Atlantic
depression known as the Canary Abyssal Plain (Heezen et al., 1959). The Madeiran
archipelago consists of the large island, Madeira itself, and a number of small volcanic
islands. Chao, Deserta Grande and Bugio. About 50 km N. E. of Madeira lies Porto
Santo and the islets of Ilheo de ponte. Peno, Baixo, Limo and Pescardo. These islands
27
C.J. HUMPHRIES
0 100 200
1. . 1 • 1
Km.
^ Porto Santo
0 /
Madeira *
Salvage Islands
-. Lanzarote
La Palma ¿/ /
A Tenerife iT ^ ^/
\J ^_ í? Fuerteventura ^
Gomera ^ \ ^ —a ¿i/ y^^""^
Gran Canana / 19
Hierro / '-^
.,. -f,,,. ,_ i •
Rabat >
] • Agadir
Sahara Desert
30 •^
Fig. 1. Sketch Map showing the location of the north-east Atlantic Archipelagoes in relation
to the African mainland.
are much more isolated than the Canarias group and border the huge Madeiran
Abyssal plain 100 km west of Morocco and 500 km north of the Western Canary
Islands. The Salvage Islands are situated between these two principal island groups
lying about 200 km north of Tenerife.
Details of the Azores and the Cape Verde archipelagos are omitted since they are
not inhabited by any species of Argyranthemum.
ECOLOGICAL DIVERSITY IN THE MACARONESIAN ISLANDS
Details of the climatic and floristic elements, and the limits of the principal
vegetation zones in the Macaronesian Islands and indeed the Canary Islands in
particular have been discussed extensively by various authors (Webb and Berthelot,
1836- 1850; Christ, 1885; Schenk, 1907; Ceballos and Ortuño, 1951; Lems, 1960;
Cifferi, 1962; Oberdorfer, 1965; Bramwell, 1971, 1972 (a); Bramwell & Bramwell,
1974) and so are only briefly summarised here. The distribution of the vegetation
zones is given in fig. 2 and Table 1 gives a summary of their characteristics.
The Canary Islands can be subdivided into two major phytogeographical regions.
The eastern islands of Lanzarote, Fuerteventura, Lobos and Graciosa which constitute
one región differ from the remainder of the archipelago in a number of ways. They
all have a low elevation (max. altitude of 650m) and a low rainfall, consequently
being very arid for much of the year. Being cióse to the African mainland, they tend
28
Fig. 2. Distribution of the main vegetation zones
in the Canary Islands, the Salvage Islands and Madeira*
^
Porto Santo
Altitude
Madeira
Desertas
^
Sf/* Salvage Islands
CD
La Palma
Tenerife
Gomera
Gran Canaria
Alpine violetum
Montane leguminous scrub
Pine savannah
Juniper scrub
Evergreen forest/tree heath
Lowland scrub
Lanzarote
Fuerteventura
Or C
o
•z
>
z
a§ w
s;
>
Q
W
C
Hierro
*Based on CebaUos & Ortuño, 1951 and Tibeiro, 1949
Table 1: Principal Vegetation Zones
co
O
Vegetation Zone
I. Macaro - alpine Violetum
II. Sub - alpine leguminous scrub
III. Pine - savannah
IV. Juniper scrub
V. Tree heath and
Evergreen forest
VI. Lowland xeropliytic scrub
Altitude
2700 - 3500
1900-2700
800 - 1900
S. slopes
400 - 600
400- 1300
0-600
(- 800)
Distribution
Tenerife
Tenerife, Gran Canaria
and La Palma
La Palma, Tenerife
Hierro, Gran Canaria
and Madeira
La Palma, Tenerife
Hierro and
Gran Canaria
Hierro, La Palma,
Gomera, Tenerife
and Madeira
All Macaronesian
islands
Habit
Monotypic perennial herb, Viola cheiranthifolia
SmaU leaved shrubs including Spartocytisus supran-ubis,
Echium wildpretii and Argyranthemum tenerifae.
Dominated by Pinus canariensis in the Canaries
but often broken down into sub - climax communities of
Chamaecytisus proliferus and Adenocarpus foliolosus.
Small leaved shrubs dominated by Juniperus phoenicea.
Predominately N. facing but on southern slopes in
climatically favourable conditions. Broad leaved,
evergreen trees and tree heaths.
Important species in this very variable zone include
stem and leaf succulents of the Euphorbiaceae and
Crassulaceae. Other prominent families include Com-positae,
Caryophyllaceae and Liliaceae.
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
to be influenced by the Saharan climatic conditions. The westem islands, however, are
situated between 200 and 360 km from the continental coast. They are much less
influenced by the Saharan conditions and have an equable oceanic climate. Their
comparatively higher elevations (almost to 4000 m on Tenerife) together with prevailing
northerly winds allows the development of a wide range of habitats in several distinct
vegetation zones.
On northern aspects the climate is fairly warm and wet throughout the year as
indicated by the presence of wet laurel forests on the mountain slopes and rich
halophyte communities along the coastal cliffs. The southern aspects tend to be
much less influenced by the prevailing north winds and are consequently arid
throughout the summer months. Here, the lowland xerophytic zone extends to greater
altitudes and intergrades directly with the pine {Pinus canariensis Chr. Smith) savannah
zone.
The distinct vegetation zonation is best seen on Tenerife (fíg. 2), the largest
and highest of the Cañarles archipela^o, which is approximately 80 km in length,
50 kms wide at the widest point and rises to almost 4000 m. Localities above 1900 m
are snow - covered for about 5 months of the year between November and April.
The predominant vegetation of this zone consists of microphyllous shrubs, which
eventuaUy extends into a monospecific Viola cheiranthifolia H. B. and K., pseudo -
alpine vegetation zone about 2700 m. The remaining vegetation zones of the islands
can be subdivided into discrete montane and lowland zones. Much of the montane
área consists of endemic Pine savannah {Pinus canariensis) but there are many other
sub - climax communities, such as Adenocarpus foliolosus (Ait.) DC, Erica arbórea
L. and Juniperus phoenicea L. scrub. The lowland xerophytic zone is extremely variable
in relation to local topographic and climatic conditions. At one extreme are the
steep, sheltered inland cliffs (laderas) principally dominated by leaf and stem - succulent
plants of the Crassulaceae and Liliaceae. At the other extreme are the Polycarpaea -
Lotetum communities on the 'coastal flats' of the east coasts of Tenerife and Gran
Canaria. Between these two extremes many other communities exist but for the most
part, the dominant vegetation of the lowland xerophytic zone consists of several
endemic stem - and leaf - succulent perennials of the Euphorbiaceae {Euphorbia L.),
the Compositae {Kleinia L.) candelabra shrubs of the Boraginaceae {Echium) and
many therophytes.
Madeira, like the western Canary Islands is very much influenced by the northern
prevailing winds. However, it does not have discrete vegetation zones but has gradual
transitions from the upland evergreen forest and subclimax Erica arbórea heath down
to the wet, coastal halophyte communities and lowland xerophytic scrub. The island
is fairly warm and wet all year round but the south facing slopes tend to be hotter
than the north facing slopes in the summer months when the streams dry up.
The vegetated Salvage Islands of Great and Little Pitón are little more than
sand banks in comparison to Madeira and the Cañarles, with various parts some-times
becoming completely covered by the sea at high tides. The halophyte com­munities
which are to be found on the rocky Great Salvage are very exposed and have
a similar climate to the lowland north - facing xerophytic zone communities of the
western Canary Islands.
31
TABLE 2:
Synopsis of classifícation of Argyranthemum acx;ording to Humphries (1975a), together
with geographical distribution and summary of ecology [Figures refer to number of each
vegetation zone given in Table 1]
Genera/Species
Argyranthemum Webb ex Schultz Bip.
Section Argyranthemum
A. frutescens (L.) Webb ex Schultz Bip.
subsp. frutescens
subsp. succulentum C. J. Humphries
subsp. gracilescens (Christ) C. J. Humphries
subsp. parviflorum C. J. Humphries
subsp. foeniculaceum (Pitard) C. J. Humphries
subsp. canariae (Christ) C. J. Humphries
subsp. pumilum C- J. Humphries
A. lemsii C. J. Humphries
A. haouarytheum C. J. Humphries & D. Bramwell
A. foeniculaceum Webb ex Schultz Bip.
A. gracile Webb ex Schultz Bip.
A. tenerifae C. J. Humphries
A. maderense D. Don
A. winteri (Svent.) C. J. Humphries
A. lidii C. J. Humphries
A. sventenii C. J. Humphries & A. Aldridge
A. dissectum (Lowe) Lowe
A. thalassophilum (Svent.) C. J. Humphries
A. callichrysum (Svent) C. J. Hiunphries
Section Sphenismelia
A. coronopifolium (Willd.) Webb ex Schultz Bip.
*Island
Distribution
T, GC, LP
T
T
T, GO
GO
GC
GC
T
LP
T
T
T
L
F
GC
H
M
SI
GO
T
Vegetation Zone
(See Table 1)
VI
VI
VI
VI
VI
VI
VI
VI-V
III - VI
VI
VI
n VI
VI
VI
VI
VI
VI
VI
VI
Ecology
open coast
coastal halophyte
distributed in coastal
habitáis
coastal halophyte
coastal cliffs
open clearing
Pine forest to coast
clifF chasmophyte
coast
coastal cliffs, sand dunes
mountains of Handia
west coast cliffs
dry south slopes
coastal
coastal halophyte
montane scrub
coastal cliff halophyte
TABLE 2: cont.
co
00
Genera/Species
A. broussonetíii (Pers.) C. J. Humphries
subsp. broussonetti
subsp. gomerensis C. J. Humphries
A. hiérrense C. J. Humphries
A. webbii Schultz Bip.
A. haemotomma (Lowe) Lowe
Section Síigmatotheca
A. pinnatifidum (L. fil.) Webb ex Schultz Bip.
subsp. pinnatifidum
subsp. succulentum (Lowe) C. J- Humphries
Section Monoptera
A. filifoliums (Schultz Bip.) C- J. Humphries
A. escarrei (Svent.) C. J. Humphries
Section Preauxia
A. adauctum (Link) C. J. Humphries
subsp. canariense (Schultz Bip.) C. J. Humphries
subsp. gracile (Schultz Bip.) C. J. Humphries
subsp. jacobaeifolium (Webb ex Schultz Bip.) C. J. Humphrie:
subsp. dugourii (Bolle) C. J. Humphries
subsp. adauctum
subsp. erythrocarpon (Svent.) C. J. Humphries
*Island
Distribution
T
GO
H
LP
M
M
M
GC
GC
GC
GC
GC
T
T
H
Vegetation Zone
(See Table 1)
V
V
V-VI
V
V
V-VI
VI
VI
III
III-VI
III-VI
III
III
III
III
Ecology
open clearings
coastal cliffs
laurel forest
coastal cliffs
widespread in lowland
and forest zones
dry scrub
montane scrub
pine forest to open scrub
montane scrub
pine forest
pine forest
Key to hlands: T - Tenerife, Go - Gomera, H - Hierro, M - Madeira, GC - Gran Canaria, F - Fuerteventura,
SI - Salvage Islands, LP - La Palma, L - Lanzarote.
C.J. HUMPHRIES
TAXONOMY AND ADAPTIVE MORPHOLOGICAL TRENOS IN ARGYRANTHEMUM
The taxonomy foUows that of Humphries, 1975 and so will not be discussed in
detail here. Table 2 gives a synopsis of the sections and recognised species together
with a brief summary of their ecology and distribution in the Macaronesian Islands.
Fig. 3 gives the distribution of the four Canary Islands sections and section Stigmato-theca
in Madeira. As can be seen they have a distinct correlation with the principal
vegetation zones. The degree of variation in morphology, distribution and ecology
differs widely from section to section. Section Argyranthemum is the most widespread,
with thirteen species distributed throughout the Canary Islands, Madeira and the
Salvage Islands. Most species occur in the lowland xerophytic zone but a few, e. g.
A. haouarytheum and A. callichrysum occur in montane áreas and A. tenerifae
can be found in the subalpine leguminous scrub of Tenerife (table 2). Section
Sphenismelia is restricted to north facing montane áreas and lowland cliffs on all of
the western Canary Islands, except for A. haemotomma which can be found on
Madeira. Most localities are situated in open laurel forest or on coastal cliffs in áreas
of considerable geological antiquity. The monotypic section Preauxia is found
primarily in pine forests of Gran Canaria, Tenerife and the broad leaved evergreen
forest on Hierro, but also extends to lowland xeric áreas in the south of Gran Canaria.
Section Monoptera is the most restricted of the genus and is confined to xerophytic
scrub communities on S. W. slopes of Gran Canaria.
Phenotypic variation of infra - sectional taxa in such characters as degree of
woodiness, habit, leaf shape and capitulum diameter can readily be explained in
terms of adaptive trends associated with ecological conditions. Support for natural
selection of highly adaptive populations is provided by examples of convergent
morphologies in species of the same and different sections which grow in habitats
of similar ecological amplitude. To explain regional responses to natural selection
a scheme is presented in Fig. 4, wherein the overall adaptive trends are derived from
a basic type.
In the Canary Islands A. broussonetti has cióse associations with Miocene basalt
rocks and relict laurel forest habits (see fig. 5) and is thought to have the least derived
morphological attributes (see p. 47). The lignified stem is shared by aU taxa of the
genus but not at all by cióse continental relatives of the Chrysanthemum complex and
is thus considered to be a relictual character state now only suited to the island
condition. Similar conclusions for other general have been reached by Meusel (1952),
Lems (1960) and Bramwell (1972 (a)). The most woody species of the genus is
A. broussonetti, presumably since it is a species of the laurel forest, which allows
growth more or less continually through the year. Consequently, the characteristic
shnibby habit of Argyranthemum is most developed in this species. Some plants of
A. broussonetii from the Anaga península on Tenerife grow up to 6 m in diameter
and up to 2 m in height. The bipinnatifid petiolate or subsessile ovate leaves are
of a very unreduced type being perhaps only one step removed from the large ovate,
more or less entire or slightly toothed leaves to be found in the most taxonomically
isolated species of the genus, A. pinnatifidum from Madeira.
From this relatively unmodified form in A. broussonetii it is possible to derive
a number of independant, adaptive morphological trends. In lowland arid environ-ments
reduction in lignification, habit, capitulum size and leaf área produces forms
of the B and C type (fig. 4), such as A. frutescens subsp. gracilescens and A. gracile
34
Fig. 3. The distribution of sections and species density in Argyranthemum
1 •
00
C71
1 + 1 (2)
3+1 (3)
Sections
Preauxia
Sphenismelia
Stigmatotheca
Argyranthemum
Monoptera
1+1 (1) 2+3 (1)
Numeráis refer to species and
those in parenthesis refer to
the number of subspecies
1 (2)
<
O r
C
H
o
z
z> a
a
w
§
2
O
m
G
C.J. HUMPHRIES
Fig. 4 Adaptive trends in Leaf shape, Habit and Capitulum Diameter
in Argyranthemum.
Species Ecology
A A. broussoneiii
Al A. adauclum subsp. jacobaeifolium
A2 A. pinnatifidum
sheltered, warm wet forest.
B A. frutescens subsp. frutescens
Cl A. folifolium
C2 A. frutescens subsp. gracilescens
C3 A. gracile
xerophytíc zone
arid, south facing slopes of
xerophytíc zone
D A. tenerifae sub - macaro - alpine zone
El
E2
E3
E4
F
G
A.
A.
A.
A.
A.
A.
pinnatifidum subsp. succulentum
coronopifolium
modérense
frutescens subsp. succulentum
adauctum subsp. adauctum
foeniculaceum
halophytíc coastal cliffs of the north
fecing slopes of the xerophytíc zone
arid, high montane regíons
low montane (xerophytíc zone) ín
sheltered ladera.
36
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
Mü.
—E
37
C.J. HUMPHRIES
Fig. 5. The Relationship between volcanic
geology and distribution of species on
Tenerife (see text)
KEY
I I Phonolytes
^ 1 Miocene basalts
Üij Pre-Caldera phonolyte
Pumice-lapilli
I * | Trachyte-phonolyte
I I I Young basalt
• A. coronopifolium
• A. tenerifae
• A. broussonetii
A. foeniculaceum
O A. gracile
"íf" After Hausen, 1955
38
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
on Tenerife, A. frutescens subsp. parviflorum, A. adauctum subsp. gracile on Gran
Canaria and A. sventenii on Hierro. Plants of very xeric conditions discontinué growth
after shedding seed at the end of spring and remain fairly inactive during the hot
summer months. They tend to be short lived and only become iignified at tiie base
of the stems. The extreme condition can be found in A. filifoUum (type C), a species
often consisting of a single, slender unbranched stem up to about 1 cm in height,
with trifid, pinnatisect, filiform leaves and extremely small flowers,
A reduction trend also occurs in taxa of subalpine and high montane environ-ments
(type D). Here, A. tenerifae and A. adauctum subsp. dugourii are unable to
grow for up to 5 months of the year owing to persistent snow cover in the Cañadas
región of Tenerife. Oíd shoots die down after flowering at the end of the year and
new ones are produced each year from low lying stems which are only woody at
their bases. The leaves of these species are both again highly dissected and tend to
have increased hairiness at the higher altitudes. The flowers are moderately small
and the plants set seed in a matter of four or five months.
In exposed north coastal áreas of the Canary Islands plants of type E (fig. 4)
with a reduced habit, pinnatilobed or pinnatifid leaves and increased succulence,
large capitula, and reduced inflorescences can be found. Characteristic species of
this type include A. coronopifoUum, A. frutescens subsps. cañariae and succulentum
and A. modérense. In very exposed places the stems can be very short or procumbent
and adpressed to the substrate. It can be seen in figs. 3 and 4 that taxa from similar
environments in different localities on one or more islands develop similar morpholo-gical
adaptations. For example, the spectacular A. broussonetii of the laurel forests
of Tenerife and Gomera is replaced in the laurel forest of La Palma byits most closely
related but nevertheless quite distinct species A. webbü. Similarly, A. adauctum
(type A l , fig. 4) is the dominant species of montane habitáis of Gran Canaria, Tenerife
and Hierro. Despite its great variability in form it is replaced in similar habitats on
La Palma by A. haouarytheum and on Gomera by the montane endemic A. callichrysum.
Species of Argyranthemwn sect. Monoptera are very distinct from all other
sections of the genus but it is quite clear that A. filifolium from the lowland xeric
Euphorbia scrub of Gran Canaria has a convergent morphology with A. frutescens
subsp. gracilescens and A. gracile from comparable arid environment on Tenerife.
Similarly, south slope upland ecotype specimens of A. adauctum subsp. dugourii from
Tenerife have frequently been named as the sub - alpine A. tenerifae on the basis of
convergent vegetative morphology when in fact both species are quite distinct when
flowering and fruiting material is available.
Other convergent pairs include the Grand Salvage coastal species A. thalasso-philum
which is superficially very similar to A. frutescens subsp. frutescens on
Tenerife and Gran Canaria, and A. winteri from the Handia mountains of Fuerteven-tura,
which closely resembles A lidii from the west facing cliffs of the Tamadaba Massif
on Gran Canaria.
MACARONESIAN PALAEOGEOGRAPHY
Extensive geological studies on the Canary Islands have recently been summarized
by Hausen (1955, 1958, 1959, 1962, 1965 and 1971) and also by Bourcart (1946).
39
C. J. HUMPHRJES
The Canary Islands combine volcanic and tectonic origins since the two major
eastern islands of Fuerteventura and Lanzarote and the islets Graciosa and Lobos
are considered to have originated from the Ifni Gap on the African mainland and the
western group to be a line of islands resulting from Eocene (or Cretaceous) to Pliocene
(and later) volcanism after continental seafloor spreading of the major continents.
Volcanic rocks overlie the eastern islands (Watkins et al., 1966; Engel et al., 1955)
and totally comprise the western islands of Gran Canaria, Tenerife, Gomera, La
Palma and Hierro. The oldest volcanic rocks have been reported from La Gomera
(Hausen, 1962) where possible Cretaceous 'basement complexes' have been exposed
in a number of localities. The youngest volcanic rocks derived from recent lava flows
have been dated most accurately from known historical eruptions. The Las Cañadas,
for example, dominating the central volcanic región of Tenerife, is a remnant of a vast
Quaternary complex resting on a basement Tertiary or Cretaceous complex. The
central cone (Pico de Teyde) has produced radial flows as recently as 1704, 1798,
and 1909 (Macfarlane and Ridley, 1968).
Recent geological records for Madeira and the Salvage islands are much more
scanty. But, like the western Canary Islands they are of truly oceanic volcanic origin
and date back to the early Tertiary or late Cretaceous periods. In the same way they
have also been covered by more recent overlays of Pliocene and later volcanic rock
(Bourcart, 1946).
PALAEOGEOGRAPHY AND DISTRIBUTION IN ARGYRANTHEMUM
In a limited way Macaronesian palaegeography helps to determine the distribution
of particular taxa and in some cases provides crude evidence for dating the origin of
some species. Thus, distinctive taxonomically isolated phenotypes occurring on oíd
rocks possibly resemble some of the earliest divergences within the genus. Species
such as A. pinnatifidwn, A. modérense, A. bwussonetii and A. foeniculaceum are
all found in habitats composed of basal rocks of relative antiquity. For example,
populations of A. broussonetii are confined entirely to the laurel forests overlying
the Miocene basalt formations of Tenerife (fig. 5) and La Gomera. Also, the present
day disjunct distribution of the cliff chasmophyte A. foeniculaceum (fig. 5) correlates
exactly with the present day distribution of Miocene basalt rocks. Between the
disjunction hes a more recent covering of Pliocene basalt and volcanic lava from the
Quaternary epoch. A. foeniculaceum was presumably once distributed throughout
the región between the two population groups but has been prevented from re-invading
the intermedíate regions simply by the drastically changed ecological
conditions and possibly by competition from species better adapted to the more
recent habitats. It is interesting that the two population groups are more or less identical
and cannot be subdivided into sepárate taxa. For this reason alone the outlined hypo-thesis
of events is favoured rather than one involving a more adaptive species inhabiting
áreas of ecological preference since all other taxa of oblígate ecology show different
morphological trends in geographically distinct population groups.
A. tenerifüe is one of the most distinctive species of Argyranthemum separated
easily from all other species by its loóse fitting triangular involucral bracts, wide
petioles and cushion habit. Its habitat in the sub - alpine reaches of Tenerife is
composed entirely of extremely young rocks produced by volcanic activity of the
40
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
Quaternary period to present day historical eruptions. A. tenerifae therefore, represents
either a relatively recent adaptation to the Cañadas región or an adaptive immigrant
now extinct in its source localities (fig. 5).
Another interesting example on Tenerife is that of A. gracile. Pliocene lava
from the eruptions of Teide has run down the mountain side to form an overlying
coastal shield on the south western platform of the island. A. gracile is almost entirely
restricted to habitats associated with this characteristic substratum whilst being absent
firom the older rocks that flank it on either side.
CYTOLOGY
All of the 16 species of Argyranthemum so far examined cytologically have the
same chromosome number, 2n= 18, and similar karyotype morphology (Humphries,
1973, 1975 (b)). The same diploid number and karyotype symmetry is common
to many other related genera within the Anthemideae and thus provides no obvious
clue to the origin or coherence of the species within the genus.
Studies of pairing behaviour of chromosomes at meiosis are much more useful
in Argyranthemum since they indícate that there is some genetic and cytological
control of population variability (Humphries, 1975 (b)). It has been shown that
significant differences in chiasma frequencies (and henee adjustments in the degree
of recombination) occur between individuáis and populations and are the principal
regulating devices for control of variability. Pioneer populations of widespread
species and isolated populations of narrow endemics such as A. filifolium and A. lidii
tend to have a high chiasma frequency and henee increased chances of recombination.
Large populations of variable species, for example A. adauctum and A. frutescens,
on the other hand, were observed to have a much lower chiasma frequency and in
some cases up to 25% of the dividing poUen mother cells exhibited a single reciprocal
translocation between non - homologous chromosomes.
The high chiasma frequency of the pioneer or specialised endemic is interpreted
to be a compensatory device for increasing flexibility in plants with depleted variability,
i. e. those which are relatively homózygous, and inversely as a conservation mechanism
for well adapted genotypes in the more variable taxa with low chiasma frequencies
and structural heterozygosity. It seems that such fluctuations in chiasma frequency
provide a very effective genetic control of variability in natural populations and henee
adaptability in a diploid genus with species of the same genomic constitution.
ARTIHCIAL HYBRIDS AND CROSSING RELATIONSHIPS
There are no previous reports of hybridisation experiments within the Anthemideae
involving species of Aryranthemum. However, accounts of artificial crosses within
other genera of the Chrysanthemum complex have indicated that many species of
quite diverse origin are fairly easy to hybridise (Shimotomai, 1933; Villard, 1970).
Wide crosses in the Matricaria L. group of the Anthemideae (Mitsuoka and Ehrendor-fer,
1972) have shown that geographically and morphologically remote genera are
quite closely related. All attempts to cross Canary Island species of Argyranthemum
with related continental genera, including Chrysanthemum L. sensu stricto, Coleos-tephus
Cass., and Tanacetum L. have failed.
41
Table 3 Fi Crossing Relationships between Canary Island
Species of Argyranthemum
-fc.
A. frutescens subsp-
"
„
„
"
"
"
A. gracile
A. haouarythemum
A. maderense
A- callichrysum
A. foeniculaceum
A. filifolium
A. broussonetii
A. adauctum
canariae
parviflorum
frutescens
gracilescens
foeniculaceurn
"
frutescens
1
2
3
4
5
6
7
8
9
10
n
12
13
14
15
16
+
+
+
+
+
+
+
+
+
+
+
+
+
-
-
1
+
+
+
+
+
0
o
+
+
0
X
+
-
-
2
+
+
+
+
+
+
X
+
+
X
+
o
-
3
+
X
X
+
0
o
+
+
+
+
-
0
4
+ Normal Fertile Hybrids (Fj)
• Abnormal weak plants
o Normal fruit, inviable seed
— Wrinkled fruit, abortive embryos
N. X poUination failures, unattempted crossed
X ^V
o o ^v
o + 0 N.
+ + + X >v
o o X X o N.
+ + o 0 + o \^
+ + 0 o + + - N.
+ 0 + X + X + X N^
+ + • + + + - . - \^
- X - - - X X - - - N.
- - - - X - X - - - - \
5 6 7 8 9 10 11 12 13 14 15 16
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
Infra - generic crosses, on the other hand produced many fertile hybrids and
results from 900 attempts of artificial hybridisations on 16 diverse populations are
summarized in Table 3. Detailed accounts of the methods and analysis of the data
are given in Humphries (1973).
The results can be briefly considered in four ways i) Crossability expressed in
terms of fruit set; ii) morphology and vitality of hybrids; iii) poUen fertility in hybrids;
iv) meiosis in pollen mother cells of hybrids.
i) Crossability expressed in terms of fruit set: Normal cypselas containing viable
embryos are not usually produced in the crosses between A. broussonetii of sect.
Sphenismelia (pop. 15) and A. adauctum of sect. Preauxia (pop. 16) ñor with species
belonging to sects. Argyranthemum (pops. 1-13) and Monoptera (pop. 14). These
Ínter - sectional crosses usually produced abortive, wrinkled fruit, but two apparently
good crosses involving female plants of A. frutescens subsp. frutescens and pollen
from A. broussonetii and A. adauctum (Table 3) had a few normal cypeselas but these
later failed to germinate.
Other crossed involving intra- and interspecific hybridisations in sect. Argyran­themum
and intersectional crossed between species of sect. Argyranthemum, A.
coronopifolim of sect. Sphenismelia (see p. 46 ) and A. fllifolium of sect. Monoptera
showed little evidence of barriers to gene exchange. The apparently random failures
which did occur and the overall general reduction of cypsela production were con­sidered
to be the result of unsuccessful pollinations rather than the result of dishar-monious
interactions.
ii) Hybrid morphology and vitality: In nearly all cases of successful crosses
the hybrids developed as normal plants of intermedíate morphology between the
parents. However, in some F^ crosses e. g. A. frutescens subsp. foeniculaceum A.
fllifolium and A. fllifolium x A. callichrysum chlorotic and dwarf individuáis were
produced. Similar individuáis were obtained in F^ generations obtained by selfing
Fi hybrids of the crossed A. ochroleucum x foeniculaceum and A. frutescens subsp.
frutescens x foeniculaceum. One F^ plant raised from the cross A. frutescens subsp.
frutescens x callichrysum produced abnormal capitula without any florets. The
involucral bracts and receptacle appeared to be fairly normally developed but were
dwarfed in comparison to other capitula having well developed florets. Plants from
the reciprocal cross when A. callichrysum was the maternal parent were completely
normal with high pollen fertility.
iii) Pollen ferility in the hybrids: The pollen fertility of the parental plants as
determined by stainability in 0.3% cotton blue in lactophenol was extremely high
producing figures for good pollen between 98% and 100%. In the vigorous hybrids
of intrasectional crosses of sect. Argyranthemum pollen fertility was similarly very high
producing good pollen results in the range of 88 - 100%. Such results indícate con­siderable
genetic affinity. The lowest figure recorded from all of the hybrids produced,
even in F2 and later generation hybrids of intersectional crosses such as A. frutescens x
A. coronopifólium was still around 60%.
iv) Meiosis in Fi and F2 hybrids: As with parental populations nine bivalents
were invariably found in all fertile hybrids. The only measurable variation seen to
occur was a slight depression of overall chiasma frequency. This suggests either
that minor 'cryptic' cytological differences exist between different populations, or more
likely that there is increased heterozygosity and varying degrees of genic imbalance
between parental genomes causing some overall effect on meiotic pairing.
43
C.J. HUMPHRIES
Table 4
Meiotic configurations in aneuploid and triploid plants of the
natural hybrid A. frutescens X A. coronopifolium
Chromosome
Number
19
27
2n Configurations
9 11+ 11
1 111 + 8 II
9 III
7 m + 2 II + 2 I
6 III+3 11 + 3 I
Frequen
30
70
16.6
16.6
16.6
Frequency Number of cells examined
18
NATURAL HYBRIDISATION BETWENN A. fruteSCenS AND A. COronopifoUwn ON TENERIFE
There are no other examples besides that between A. frutescens and A. corono­pifolium
of natural hybrids occurring between neighbouring populations of different
taxa in Argyranthemum. In this isolated, intersectional cross, hybrids have only
developed since the formation of scree slopes from material produced by tunnelling
30'N
Buenavista
Fig. 6. Sketch map of the Teño región Tenerife, showing the collection sites for Argyranthemum
frutescens (A), A. coronopifolium (C) and their hybrids (B).
44
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
6 ,
6
"o
•a
10
9 ^
8 .
7 '
6 •
r
Population €
i<W-Am
o 5-6.9 cm.
/*\ 6-8.6 cm.
(~\ cypsela length 2.9-4.1 mm.
O * 4.2-5.4 mm.
f'^ 5.5-6.7 mm.
6-
oi- » *-é-
9
\
O- 3-
3
3
(h.
¿-
Involucre diameter mm.
10 11 12 13 14 15 16 17 18 19 20
Fig. 7. Variability in natural populations of Argyranthemum frutescens
A. coronopifolium /'"N and their hybrids O 3
activities on Tenerife, through the Teño cliffs connecting the Teño promontory with
the Buenavista región (fig. 6). The hybrid population has developed since the construc-tion
of the tunnel in 1965 (and it is significant that no pre 1965 coUections of the hybrid
seem to exist) and is restricted entirely to the disturbed scree slope which is found
45
C.J. HUMPHRIES
directly between the two parental populations — the cliff populations of A. coronopi-folium
and the coastal populations of A. frutescens. To show the intermediacy of the
hybrid population, pictorial representation of variation in four characters /. e. petiole
width, leaf length, involucra! diameter and cypsela length is given in fíg. 7. The long,
wide, pinnatilobed leaves, with characteristic cuneiform petioles, wide capitula and
large ray cypselas provide reliable data for separating A. coronopifolium from
A. frutescens, which has comparatively much dissected leaves, narrower petioles,
smaller capitula and generally shorter ray cypselas.
Examination of chromosomes in pollen mother cells from buds collected in the
fíeld show that all naturally occurring hybrids are diploid (2n =18) with normal
pairing of 9 bivalents at meiosis. However, in root tips from cultivated plants raised
from wild hybrid cypselas, the range of somatic mitotic chromosome numbers varied
between 2n= 18 and 2n = 36 (Humphries, 1975 (b)). Pairing at meiosis in pollen
mother cells of triploid individuáis showed a large number of trivalents, several
bivalents and only one or two univalents suggesting considerable genome homology
between the parents (table 4). The absence of aneuploids in natural populations
suggest that even in disturbed habitáis, selection pressures are still very strong and
suffícient to elimínate such plants. This was also reflected in the observations that
many cypselas cultivated in the greenhouse failed to germinate and several chlorotic
seedlings which did emerge died within a few days.
DISCUSSION: PATTERNS OF EVOLUTION
On the basis of the evidence just presented, the species of Argyranthemum are
a monophyletic assemblage of active epibiotics of warm termperate, Oíd World,
possibly Mediterranean derivation. The exact relationship of Argyranthemum with
Chrysanthemum L. s. s. and other genera is difñcult to ascertain since all attempts
to produce intergeneric hybrids with their nearest relatives have so far failed. Similarly,
the evolutionary relationships of sections and species in the genus are no less difñcult
to demónstrate, but there is little reason to doubt that most diversifícation has taken
place in the Macaronesian Islands. Perhaps the most intriguing question concerning
the origin of Argyranthemum is which of the contemporary forms most resembles
the immediate ancestors. Other well documented examples of adaptive radiation have
been based on shizo- or patroendemic groups, e. g. Aeonium (Lems, 1960), Sonchus
and Echium (Bramwell, 1971, 1972 (a)) where it is possible to arrange species
groups into putative phylogenies on the basis of life - form sequences. For example
in Aeonium, Lems (1960) has considered the ancestral (or least derived) species to
be tall, woody, slow growing sparsely branched perennials with large inflorescences.
The direction of evolutionary trends is assessed by relating variation in growth form
with non - endemic members of the genus. Those species or sections which are endemic
to the Macaronesian islands and are clearly different from non - endemic taxa are
believed to be derivative groups. Thus, in Aeonium divergent growth forms have
resulted from a number of different lines towards low - growing, herbaceous annuals,
large - leaved monocarpic biennials, compact bushes and sprawling, hanging cliff
plants with small inflorescences.
As Argyranthemum is endemic to the Macaronesian islands and cannot be
considered to be directly derived from Chrysanthemum or any other genera of the
46
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
Anthemideae it is impossible to determine directions of evolutionary trends by
comparison to continental taxa. The most fruitful systematic evidence for speculation
of the evolutionary situation in Argyranthemum comes from the relationship between
morphology, ecology and palaeogeography. For this approach it is assumed that
ancestral taxa carne to the Macaronesian islands associated with other (now relict)
migrants. Therefore, species of section Sphenismelia restricted to relict habitats and
associated with laurel forest and halophyte relicts together with the monotypic section
Síigmatotheca (A. pinnatifidum) of Madeira occurring in similar habitats, probably
possess the highest number of ancestral character states for the genus. Features
these two sections have in common include thick woody stems, large, glabrous,
sessile or shortly petiolate leaves, large capitula with conspicuous white ray florets
and winged disc cypselas.
It is possible then to suggest that one derived evolutionary line has given rise
to A. adauctum (sect. Preauxia) with pubescent, sessile pinnatisect leaves, small
capitula and wingless cypselas. This species has a predominantly montane distribu-tion
in habitats of relatively recent origin. Other Unes have given rise to species of
sections Argyranthemum and Monoptera. Section Argyranthemum is the most diverse
of the genus with 13 species distributed through a whole range of habitats and developed
in response to relatively arid environments and varied geological conditions. Principal
morphological features of this section as distinct from sect. Sphenismelia include
glabrous pinnatilobed to pinnatisect leaves, smaller capitula and reduced habit. Section
Monoptera represents a very specialised group of two species adapted to arid conditions
on Gran Canaria. Its obvious adaptive features include a much reduced life cycle,
reduced lignification, highly dissected more or less filiform leaves and extremely
small capitulas.
From the crossing data it would appear evident that more than one coenospecies
is present within the genus. It is also abundantly clear however, that despite a wide
range of variation in morphology and eco - geographic localisation, the ability to
exchange genes in very divergent taxa still remains.
Cytological studies on the pairing behaviour of chromosomes in parental and
hybrid populations suggest that population differences within and between taxa result
from genic changes rather than by major chromosomal reorganisation. Should there
have been even minor structural chromosome differences between species such as
inversions or translocations one would have expected at least to fmd a considerable
decrease in pollen fertility. The high fertility valúes in Argyranthemum in all hybrids
endorses the possibility of high chromosomal homology between different taxa. The
formation of gametangial defects preventing pollen formation in some natural F2-6
hybrids of A. frutescens x coronopifolium and floretless individuáis of the synthesised
hybrid A. frutescens x callichrysum maintains the idea that differentiation has proceeded
at the genic rather than the chromosomal level.
The behaviour of chromosomes at meiosis in F2 aneuploids of the intersectional
A. frutescens x coronopifolium hybrids is similar to species of autopolyploid origin.
This fact, together with regular bivalent pairing at meiosis in all other fertile synthesised
hybrids, is in keeping with the interpretation that divergence is a result of adaptation
by natural selection of variants derived from a common genomic stock. Many taxa
are thus potentially interfertile and intemal (post - zygotic) isolating factors play
little, if any, role in keeping species apart. This is shown plainly by the fact aht
natural hybrids are produced only when the natural habitat is severely disturbed near
47
C.J. HUMPHRIES
the zone of contact of populations of different taxa; in such circumstances hybrid
swarms are readily produced indicating that pollen flow is common even though
gene flow is rare. External (pre - zygotic) isolating mechanisms in Argyranthemum
are entirely the result, it seems, of ecológica! differentiation and despite the archipelagic
situation there is little direct evidence to show that geographical isolation has played
a critica! ró!e in speciation. That such a wide range of adaptive forms can exist within
the Macaronesian isiands depends not only on the diversity of the habitat but also on
steep ecológica! gradients with very narrow ecotones between habitáis which have
remained stable over long periods of time. Evidence for stabiüty is shown by the surviva!
of reüct palaeoendemics in the Canary Isiands such as Dracaena draco L., Bencomia
Webb and Berth. and Marcetella Svent. and the patroendemics Lauras L. and
Adenocarpus DC. Evidence for steep ecológica! gradients comes from a general
absence of hybrids between widespread active epibiotics such as Argyranthemum,
Aeonium, Echium and Sideritis L. In a!l these cases hybrids only occur readily in
locaüties of considerable disturbance.
SUMMARY
1) The genus Argyranthemum (Compositae: Anthemideae) is centred in the
Canary Isiands, where 18 of the 22 species are found in 4 of the 5 principal vegetation
zones. 3 other species are found in the. Madeiran archipelago and one is endemic
to the Salvage Isiands.
2) The genus, of probable early Tertiary origin, presents an example of mono-phyletic
adaptive radiation. With respect to morphology the most adaptive characters
include woodiness, habit, leaf shape and dissection, and flower size. At one extreme
species form dense, very ügnifíed long - üved shrubs with large leaf área and large
capitula, whilst at the other extreme slender single - stemmed species with reduced
life cycle, slight woodiness and very dissected leaves are found. The genus can be
divided up into 5 discrete sections on the basis of cypsela morphology.
3) The distribution of the 5 sections closely correlates with the principal vege­tation
zones and they are therefore considered to represent oíd divergences. Species
of sections Sphenismelia and Stigmatotheca probably possess more ancestral morpholo-gical
atributes than species of sections Argyranthemum, Monoptera or Preauxia, an
assumption based on the ecogeographical and palaeogeographica! associations.
4) Each species consists of morphologically discrete but genetically related,
isolated populations forming a 'Rassenlcreislehre' distribution.
5) Evolution has been a gradual process (al! species are diploid) by strong
natural selection of adaptable genotypes in steep ecológica! gradients. Isolation
between different species has been influenced entirely by extrinsic ecológica! and
possible geographical factors. Genetic isolation has proceeded only by accumulation
of disharmonious genes and has lagged a long way behind morphologica! and
physiologica! divergence.
6) Each population has a clear selective advantage in the habitáis in which it
occurs. Hybrids are formed only in áreas of massive disturbance despite the evidence
that considerable gene transfer exists between adjacent populations.
48
EVOLUTION AND ENDEMISM IN ARGYRANTHEMUM
ACKNOWLEDGEMENTS
Most of the work for this paper was carried out whilst holding an SRC studentship
at the Department of Botany, University of Reading. My sincere thanks go to Professor
V. H. Heywood and Dr. D. M. Moore, who have provided the necessary facilities
and guidance throughout the course of the work. Financial support for field studies
has come from the University of Reading Research Board, the Science Research
Council and the Godman Fund (BMNH), for which I am most grateful.
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