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Systematics and Phytogeography |
2Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom; 3Institute of Cell and Molecular Biology, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh EH9 3JH, United Kingdom; 4Royal Botanic Garden, 20A Inverleith Row, Edinburgh EH3 5LR, United Kingdom
Received for publication July 26, 2001. Accepted for publication November 8, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: Adenocarpus • biogeography • Fabaceae • Genista • Genisteae • island endemism • Macaronesia • molecular phylogeny • radiation • Teline
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). They are notable for having a particularly confused generic taxonomy. There are several well-established genera, such as Cytisus and Genista, but little agreement as to which segregates of these genera are valid (Polhill, 1976
; Bisby, 1981
). Recent molecular studies have shown the Genisteae to be monophyletic (excluding Melolobium and Argyrolobium uniflorum; Käss and Wink, 1995, 1997
), but further sampling is needed to resolve the generic classification.
The Genisteae are well represented in the Canary Islands and Madeira, with 22 native species in six genera (see references in Table 1). In Madeira there are three endemic species (Teline maderensis, T. paivae, and Genista tenera) and one possibly native, nonendemic species (Adenocarpus complicatus). The situation is more complicated in the central and western Canary Islands (Fig. 1) where some groups appear to have undergone adaptive radiations. There are no native representatives on the dry, eastern islands (Fuerteventura and Lanzarote). The genus Teline is represented by ten endemic species and Adenocarpus by three endemic species (one of which, A. ombriosus, is considered to be close to extinction [Santos-Guerra, 1996
]). The two common Adenocarpus species (local name is "codeso") are ecologically important, in places forming the dominant vegetation. A good example is found in the "codesales" of high altitude areas of La Palma (Genisto benehoavensis-Adenocarpetum spartioidis A. Santos). Teline canariensis (the local name of which is "retamón") is a prominent component of the fayal-brezal (Myrico fayae-Ericion arboreae Oberdorfer) vegetation on Tenerife, and T. stenopetala ssp. stenopetala (the local name of which is "gacia") is cultivated in the islands for fodder (Pérez de Paz et al., 1986
). Genista, however, is represented by a single endemic species (i.e., G. benehoavensis) reported as extremely rare in the 1970s (Santos-Guerra, 1975
) but recently part of a successful conservation program in the high elevation zone of La Palma (Palomares Martínez, 1997
). The remaining genera consist of Spartocytisus (an endemic genus with two species), Chamaecytisus (one variable endemic species), and Retama (a single, nonendemic species). The Adenocarpus, Genista, and Teline species have been the subject of much generic revision (see Table 1) and have been revised by Gibbs (1967, 1974)
, Gibbs and Dingwall (1972)
and del Arco Aguilar (1982, 1983, 1993)
. These treatments, with minor modifications, have been followed here.
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; Kim et al., 1996
; Francisco-Ortega et al., 1997a
; Panero et al., 1999
; Vargas, Morton, and Jury, 1999
; Helfgott et al., 2000
). Biogeographic links for the Macaronesian flora are diverse. There is evidence for Eurosiberian (Saxifraga [Saxifragaceae]; Vargas, Morton, and Jury, 1999
), Mediterranean (Argyranthemumi [Asteraceae], Bencomia [Rosaceae]; Francisco-Ortega et al., 1997a
; Helfgott et al., 2000
), Southern African (Phyllis [Rubiaceae]; Sunding, 1979
), North and East African (Dracaena [Agavaceae]; Sunding, 1979
) and New World (Pericallis [Asteraceae]; Panero et al., 1999
) origins, as well as Asian and Australasian disjunctions (Apollonias [Lauraceae], Picconia [Oleaceae]; Sunding, 1979
). The ITS (internal transcribed spacers)-5.8S region often fails to provide adequate sequence divergence for phylogenetic resolution of rapid and recent speciation, with many examples for island groups (Böhle, Hilger, and Martin, 1996
; Kim et al., 1996
; Helfgott et al., 2000
), and in particular the highly conserved 5.8S region is often uninformative in such studies. The objectives of this study were: (1) to examine phylogenetic relationships of the Macaronesian Genisteae; (2) to determine whether the Canarian Genisteae share a common biogeographic origin (i.e., European, Mediterranean, or African); and (3) to investigate the biogeography of Teline within the Canary Islands. This study is part of an ongoing project concerning the biology of Canarian Genisteae; in a separate paper, one of us (Percy, in press) also reports some aspects of the ecological relationships of Macaronesian Genisteae and endemic species of plant feeding psyllids (Hemiptera). It is hoped that a robust phylogeny for the endemic legumes may shed light on patterns of speciation in their associated insects.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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to have originated from within the Cytisus-group. To shed further light on the origins of these species would require extensive sampling among the cytisoid legumes, which was beyond the scope of this study. Fourteen species of Teline were sampled, representing the entirety of the genus as usually circumscibed (section Teline) with the exception of the restricted endemic T. osmariensis (Coss.) P. E. Gibbs & Dingwall, from Morocco. This species, known only from two collections, is described as showing close affinity to T. monspessulana (Gibbs and Dingwall, 1972
; Maire, 1987
). Two Spanish species recently transferred (Talavera and Gibbs, 1999
) from Cytisus to a separate section of Teline (section Chronanthus: T. patens (DC.) Talavera & P. E. Gibbs and T. tribracteolata (Webb) Talavera & P. E. Gibbs) are not considered to be closely related to the Macaronesian species and have not been included here. The majority of intraspecific taxa in the Canary Islands, including all five subspecies of T. stenopetala (the most variable species), were also analyzed, the only exceptions being the very rare T. rosmarinifolia subsp. eurifolia del Arco and a recently described subspecies, T. pallida subsp. silensis del Arco (del Arco Aguilar, 2000)
. Eleven of the 15 Adenocarpus species, representing each of the three to five species groups delimited by Lems (1958)
, Gibbs (1967)
, and Maire (1987)
, were used to determine the affiliation of the Canarian taxa. The distinctive basal cytisoid plant, Argyrocytisus battandieri, which Talavera and Salgueiro (1999)
have suggested should be placed in Adenocarpus, is also included. Finally, a number of Genista spp. (7 of about 80 spp.) from a wide geographical range in Africa and Europe, as well as different morphological types (unifoliolate and trifoliolate), were chosen to investigate the biogeographic origins and monophyly of the island species of Genista and Teline and to ascertain the specific affiliation of G. benehoavensis from the Canary Islands. Details of all the taxa sampled and location of voucher specimens have been archived at the Botanical Society of America website (http://ajbsupp.botany.org/v89/). In order to provide rooting of the tree, we used a member of a related leguminous tribe (Thermopsideae) as the outgroup (Anagyris foetida). An unrooted analysis without Anagyris was used to check that this outgroup did not affect the topology of the ingroup, in view of the divergence of Anagyris from the ingroup.
Molecular procedures
A total of 50 individuals, representing 36 species, were sampled, mostly from field-collected leaf material (vouchers in GL = University of Glasgow Herbarium). However, herbarium material was used for Adenocarpus mannii (E = Royal Botanic Garden Edinburgh Herbarium), A. ombriosus (TFC = Herbario de la Universidad de La Laguna, Tenerife) and Teline stenopetala subsp. microphylla (from La Gomera) (E). In addition, leaf material was obtained from a cultivated, wild-origin specimen of Genista tinctoria (RBGE = Royal Botanic Garden Edinburgh). DNA was extracted from silica-dried leaf material using a QIAGEN DNeasy Plant Mini Kit (Qiagen, Crawley, West Sussex, UK).
Amplification of the ITS1–5.8S rDNA-ITS2 region was accomplished using forward primer ITS 5p: 5'-GGAAGGAGAAGTCGTAACAAG-3' (Möller and Cronk, 1997
) and reverse primer ITS 4: 5'-TCCTCCGCTTATTGATATGC-3' (White et al., 1990
). However, the amplification of A. mannii from herbarium sheets dated 1968 (Tanzania) and 1981 (Malawi) and A. ombriosus (specimen dated 1985) required the use of internal primers to sequence ITS1 and ITS2 independently. In this instance, ITS1 was amplified using primers ITS 5p and ITS 2p: 5'-GCTACGTTCTTCATCGATGC-3' (Möller and Cronk, 1997
), and ITS2 was amplified with a forward primer we designed using sequences already obtained (ITS 2-LEG: 5'-GCAGAATCCCGTGAACCAT-3') and primer ITS 4. The primer ITS 2-LEG may also give improved amplification of the ITS2 region, over conventional primers, for other papilionoid legumes. Each polymerase chain reaction (PCR) cycle comprised denaturation at 94°C for 4 min, followed by 30 cycles of 94°C for 30 s, annealing at 58°C for 1 min, and an extension of 72°C for 1 min, with a final extension of 72°C for 10 min. Amplified PCR products were purified with a QIAGEN QIAquick PCR Purification Kit (Qiagen), and resuspended in 30µL of H2O for direct sequencing using an automated ABI 377 (Perkin-Elmer, Applied Biosystems, Warrington, UK). All the sequences referred to here have been deposited in GenBank database under the accession numbers GBAN-AF330637–GBAN-AF330686. (The prefix GBAN- has been added to these accession numbers to link the online version of American Journal of Botany with GenBank but is not part of the actual accession number.)
Sequence analysis
Sequence boundaries for ITS1-5.8S-ITS2 regions were determined with reference to data for Vicia faba (Yokota et al., 1989
) and previous sequences for the Genisteae (Käss and Wink, 1997
). Alignment of sequences was straightforward and was done manually using the program Se-Al (version 1.0a1; Rambaut, 1998
). A single ambiguous region of 3 base pairs (bp) in ITS1 (position 219–221 of the aligned matrix) was excluded in a test analysis, but with no change of topology, so the final analysis was run on the complete matrix. The remaining insertion/deletion events (indels) were unambiguous and small (1–3 bp), with the exception of one notable 17-bp deletion in the ITS1 region of Genista cinerea and G. ramosissima (position 103–119 of the aligned matrix). The length range of ITS1 was 219–241 bp, and ITS2 was 217–221 bp, while 5.8S was uniformly 163 bp without gaps. Features of the aligned matrix are given in Table 2. The aligned matrix is available from GenBank and the aligned matrix and trees (Figs. 2 and 3) are available from TreeBASE (http://www.herbaria.harvard.edu/treebase/).
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). The following heuristic search parameters were employed for the maximum parsimony (MP) analysis: 1000 random stepwise addition replicates with tree bisection reconnection (TBR) branch swapping, MULTREES, and COLLAPSE. Bootstrap analyses were performed using 2000 simple addition replicates with TBR branch swapping, and decay indices (Bremer, 1988
) were calculated using AutoDecay (version 4.0; Eriksson, 1998
) and PAUP*. The analyses were run either with gaps coded as missing or treated as present/absent in a separate binary matrix using contiguous and simple indel coding (Simmons and Ochoterena, 2000
). A maximum likelihood (ML) analysis was performed for a comparison to the maximum parsimony (MP) results. Parameters and assumptions used in the ML search were selected using program Modeltest (Posada and Crandall, 1998
). The two models selected were Tamura-Nei with gamma distribution, and general time-reversible (GTR) with invariable sites and gamma distribution, the latter selected on the basis of the Akaike information criterion (AIC) (Akaike, 1974
). Both these models produced the same tree but the GTR model had a slightly improved (lower) log-likelihood score. Maximum likelihood heuristic search parameters were simple addition sequence of taxa with TBR branch swapping, MULTREES, and COLLAPSE. To examine the possible polyphyletic origin of Teline, MP and ML analyses were run with the monophyly of Teline constrained for (a) a monophyletic Macaronesian clade, (b) a monophyletic genus, and (c) a paraphyletic clade with the inclusion of Genista segonnei. The monophyly of an apparently paraphyletic T. stenopetala (with and without subsp. spachiana) was also examined. The nonparametric Templeton's Wilcoxon signed-rank test, as implemented in PAUP*, and log-likelihood scores were used to assess these assumptions by testing significant length differences between constrained and unconstrained trees (Table 3).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Phylogenetic results
A maximum parsimony analysis produced a single tree of length 318, a consistency index (CI) of 0.643 (excluding uninformative characters), and a retention index (RI) of 0.882, which had an identical topology to the tree recovered using ML analysis. Coding gaps as a separate binary matrix provided a single synapomorphy grouping Teline salsoloides with T. stenopetala subsp. spachiana, within an otherwise totally invariable T. canariensis clade. Another single indel grouped the three Adenocarpus complicatus samples in an otherwise invariable complicatus/Canary Island group. Two trees were recovered in an MP search without Anagyris. One of these differed from the tree presented, but only by a single change, which was the reverse placement of Genista florida-G. tinctoria in relation to the G. segonnei-T. linifolia group. Midpoint rooting gave the same root as that provided by Anagyris.
The ITS region provides sufficient resolution of the majority of continental species/group relationships but divergence is insufficient to resolve with confidence the island species groups (Figs. 2 and 3). Nevertheless, the phylogeny provides 15 nodes (excluding intraspecific nodes) with bootstrap support 
75% and six nodes with decay indices 5, from which a number of conclusions can be drawn on the relationships between island and continental taxa and relationships between island groups.
Genista
The molecular results support the transfer to Genista of Cytisus benehoavensis by del Arco Aguilar (1982)
, and moreover places this Canary Island species together with the Madeiran species, G. tenera, in section Genista with the type species, G. tinctoria (bootstrap = 96%). It is interesting that the members of this clade (G. benehoavensis, G. tinctoria, and G. tenera) all have a small or vestigial aril (Gibbs, 1974
; del Arco Aguilar, 1982
). The data also support the transfer to Genista of Adenocarpus segonnei (Gibbs, 1974
) and strongly suggests (bootstrap = 93%) affinity within Genista to the Teline linifolia group.
Adenocarpus
The data analysis support the finding of Käss and Wink (1997)
of the very close relationship between A. foliolosus and A. viscosus of the Canary Islands with the European A. complicatus (bootstrap = 93%). Our data further show that a third Canarian species not sampled by Käss and Wink (1997)
, A. ombriosus, has identical sequence to A. foliolosus and A. viscosus. Within Adenocarpus as a whole there appear to be three subgeneric groups (although the anagyrifolius group is not strongly supported; bootstrap = 55%). There is support (bootstrap = 78%) for a bracteate clade (species possessing distinct and persistent floral bracts) including A. nainii, A. boudyi, and A. telonensis. Adenocarpus nainii has previously been treated as a subspecies of the weakly bracteate A. complicatus (with narrow floral bracts, present when the inflorescence is in bud but rapidly caducous on maturation and extension of the inflorescence). Adenocarpus mannii occurs in montane regions of tropical Africa and is of biogeographic interest as sister to the Mediterranean/Canarian A. complicatus-viscosus-foliolosus group (bootstrap = 82%).
Teline
Our data show that the genus Teline is polyphyletic, contrary to cpDNA (rbcL) results presented by Käss and Wink (1995)
, in which Teline is apparently monophyletic. With the more comprehensive sampling in this study, forcing Teline to be monophyletic results in an extra tree length of ten steps, a significantly longer topology (p = 0.05; Table 3). Teline has been considered of genistoid affinity (Polhill, 1976
; Bisby, 1981
; Norverto, González-Andrés, and Ortiz, 1994
; González-Andrés and Ortiz, 1995
) and we confirm that Teline is nested within Genista, as shown by Käss and Wink (1997)
. There therefore seems little reason, other than traditional taxonomic practice, to maintain the genus separate from Genista. Each of the two clades of Teline ("linifolia clade" and "monspessulana clade") are monophyletic, with independent origins within the genus Genista, and each representing separate colonizations of the Canary Islands. The continental species, T. linifolia, distributed in the western Mediterranean including northwest Africa, is the sister taxon to the island linifolia group. The more widespread continental species, T. monspessulana, which has a circum-Mediterranean distribution and occurs in the Azores, is possibly sister to the island monspessulana group (but see further discussion below on the biogeography of Teline). The Madeiran Teline species are in the "monspessulana clade."
Within the island linifolia group, T. pallida from Tenerife is more closely related to T. nervosa and T. rosmarinifolia from Gran Canaria (bootstrap = 78%) than to the conspecific T. pallida ssp. gomerae (P. E. Gibbs & Dingwall) del Arco, from La Gomera. Within the island monspessulana group, one of the five subspecies of T. stenopetala, subsp. spachiana, is identical in sequence to T. salsoloides and differs from T. canariensis and T. osyroides by a single indel. The four Tenerifean taxa (T. canariensis, T. osyroides, T. salsoloides, and T. stenopetala subsp. spachiana) form the homogeneous canariensis group (bootstrap = 99%), which are distinct from the remaining four subspecies of T. stenopetala. Even excluding subsp. spachiana, T. stenopetala is paraphyletic in this analysis. However, constraining T. stenopetala to be monophyletic (excluding subsp. spachiana) requires an additional tree length of only two steps, which is not significant (Table 3). One should therefore interpret these results cautiously, as there is the possibility that gene flow in the "monspessulana clade" is confounding phylogenetic signal, and this risk is increased by the human introduction and movement of species (Francisco-Ortega et al., 1997b
; Clarke, Johnson, and Murray, 1998
).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Sunding, 1979
; Francisco-Ortega et al., 1997a
; Helfgott et al., 2000
). The most northern part of Morocco shares many floristic links with southern Europe (Valdés, 1991
). However, this eu-mediterranean element is currently almost completely absent from the northwestern part of Africa (southwestern Morocco) closest to the Canary Islands.
As the Canary Islands are oceanic in origin (Carracedo et al., 1998
), long-distance dispersal is required. The Canarian Genisteae, which requires at least seven colonization events to account for 18 species (including the three genera not included in this study), have been relatively successful at distance dispersal. Quézal (1978)
and Hooghiemstra et al. (1992)
provide evidence for a southward extension of Pleistocene Mediterranean woodland along the northwest edge of Africa, which would have considerably lessened the present-day disjunction (arrow B in Fig. 4). Even so, seeds would still have needed to travel more than 200 km to reach suitable habitat on Gran Canaria. Wind, bird, and sea dispersal may all have been promoted by prevailing northeasterly trade winds and sea currents that were accentuated during the Pleistocene (Rognon and Coudé-Gaussen, 1996
) (arrow A in Fig. 4). The Genisteae have an explosive dehiscence: seeds are ejected from the pod, which remains attached to the parent plant. These plants have no obvious adaptations to dispersal by air or water. Mature seeds of all genera of Canarian brooms typically sink immediately in sea water (D. M. Percy, personal observation). Endozoochorous bird dispersal is a more likely means by which brooms of Mediterranean origin may have reached the Canary Islands. The endemic avifauna of the Canary Islands is predominantly Palaearctic, with central European and Mediterranean affiliations (Bacallado, 1976
), and European migrants occur as vagrants.
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that the latter four species form a group of vicariant species. Secondly, there is the bracteate group which is mainly confined to northwest Africa (Morocco and Algeria). The exception is A. telonensis, which has a range extending from northern Morocco to southern Iberia and France. The bracteate group is predicted to include three species additional to those sampled here: A. cincinnatus, A. umbellatus, and A. faurei, which share similar morphological traits (Gibbs, 1967
).
The Canarian species belong to the third group, which is otherwise comprised of the polymorphic species A. complicatus (subsp. complicatus sensu Gibbs, 1967
) and A. mannii, which occurs only in tropical and subtropical Africa. Adenocarpus complicatus is widespread across southern Europe to Turkey and Syria, localized in Algeria, and also present on Madeira. This species has a controversial taxonomic history with a number of separate species recognized by different authors (Castroviejo, 1999
) as well as numerous intraspecific varieties (Rivas-Martínez and Belmonte, 1989
). The lack of molecular divergence between the Canarian and European taxa implies a rapid and widespread expansion of this group, which contrasts with the relatively localized distributions and greater divergence in the other two Adenocarpus groups. The Canarian species are therefore considered part of a recent expansion of A. complicatus in southern Europe.
It is interesting that A. mannii also exhibits considerable morphological variation throughout its range but no sequence divergence was found between samples from Malawi and Tanzania. Two migration routes (arrows A and B in Fig. 5) have been suggested to explain the presence of European and Mediterranean elements in the montane tropical African flora (Quézel and Martinez, 1958–1959
; Wickens, 1976
; Quézel, 1978
). The absence of A. mannii or A. complicatus in the Moroccan Atlas suggests that the Morocco-Sahara track (shown by Quézel and Martinez [1958–1959] to have had a Pleistocene extension of Mediterranean woodland; arrow A in Fig. 5) is not the route by which A. mannii reached central Africa. Instead, the close relationship with A. complicatus and the presence of the latter species around the eastern Mediterranean makes the Red Sea hills migration route (arrow B in Fig. 5) put forward by Wickens (1976)
a reasonable alternative hypothesis. Subsequent migration of A. mannii to west Africa may have followed the southern migration route (arrow C in Fig. 5) proposed by White (1993)
.
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A geographical division is evident in the phylogeny between the central and western island groups. This is particularly evident in the T. linifolia clade, which has a subclade of three species endemic to the central islands (Gran Canaria and Tenerife) while the remaining two species are restricted to the western islands (La Gomera and La Palma). In the T. monspessulana clade the situation is more complex, but the T. canariensis group and T. microphylla occur only on the central islands, while all the subspecies of T. stenopetala are native only on the western islands. One possible explanation for this east-west vicariance, that is consistent with the phylogeny presented here, is that (in both cases) an original colonization of the relatively old island of La Gomera, which is 10–12 million years old (myr) was followed by two independent further colonizations from La Gomera of (1) the central islands and (2) the younger western islands (La Palma and El Hierro; 1–2 myr). This scenario would accord with the basal position of La Gomera species in both Teline clades.
Island evolution and different patterns of radiation
Each of the main groups of Canarian Genisteae shows a different pattern of species diversification. These may be summarized as follows.
The Teline monspessulana clade
Geographical segregation within this clade indicates that interisland dispersal has been less frequent than diversification within islands. Diversification within islands is, in turn, linked to island size and habitat diversity. Thus, the most morphological diversity in Teline can be found on Tenerife (the most ecologically diverse island) between the five members of the T. canariensis group, but this morphological diversity is coupled with the least genetic divergence. The T. canariensis group may therefore represent a recent radiation on Tenerife after the main central volcanic and island building period, 1–2 mya (Ancochea et al., 1990
). In contrast, T. stenopetala (excluding subsp. spachiana), which is probably a paraphyletic taxon, currently has four to five subspecies on three islands that exhibit greater genetic divergence but less morphological diversity than the T. canariensis group.
The Teline linifolia clade
Radiation of this clade in the Canary Islands is less extensive than the "monspessulana clade." Interisland dispersal has apparently been more frequent than diversification within islands, with all species endemic to a single island (typically localized or rare in distribution).
Adenocarpus
The two widespread taxa are distributed in similar altitudinal and ecological niches on different islands as opposed to the geographical/island circumscribed distribution in the Teline groups. Adenocarpus viscosus occurs only on the high islands (Tenerife and La Palma) in the subalpine zone and generally more xeric habitats, while A. foliolosus occupies a lower altitude, more mesic niche on four of the five islands with this habitat. There are also extensive hybrid zones that have developed in locations where these habitats intergrade and often in recently disturbed "hybrid habitats" (Lems, 1958
).
Teline and Adenocarpus display a contrast between "single island lineages" (Teline) and interisland species or "horizontal lineages" (Adenocarpus) suggested for other groups (Francisco-Ortega et al., 1992
; Francisco-Ortega, Jansen, and Santos-Guerra, 1996
; Kim et al., 1996
).
Genista
The monotypic island endemism of Genista contrasts with the Teline and Adenocarpus radiations. Neither Genista species in Madeira nor the Canary Islands has undergone any diversification or radiation.
Taxonomic implications
Adenocarpus as delimited here is clearly a monophyletic genus (bootstrap = 87%). The proximity of Argyrocytisus battandieri (a genus typically placed near Cytisus) in the tree topology suggests a more cytisoid than genistoid affinity for Adenocarpus (Badr, Martin, and Jensen, 1994
). However, a recent reclassification of Argyrocytisus battandieri in Adenocarpus has been proposed due to the occasional presence of glandular papillae on the fruit surface (Talavera and Salgueiro, 1999
). The limited sampling here, together with low bootstrap support (55%) grouping Argyrocytisus with Adenocarpus, does not allow us to confirm this classification, and the phylogenies presented by Käss and Wink (1997)
do not provide an unambiguous placement of Argyrocytisus battandieri. Within Adenocarpus the molecular analysis shows that A. nainii is clearly distinct from European A. complicatus, and we therefore revert to former taxonomic treatments in recognizing this taxon at specific rank (Maire, 1922
).
Teline maderensis has more recently been circumscribed to include T. paivae (del Arco Aguilar, 1983
; Cannon and Turland, 1994
), but as these two species appear to be distinct in the molecular analysis, we have reverted to recognizing two separate Teline species on Madeira. Similarly, it seems appropriate to revive the name T. gomerae (Kunkel, 1975
) in place of T. pallida subsp. gomerae, due to the apparent polyphyly of the Teline pallida subspecies. Teline stenopetala subsp. spachiana, originally described as "Genista (Teline) spachiana" by Webb (1845)
, was later synonomized with T. canariensis by Gibbs and Dingwall (1972)
, who cited the intergradation of the two taxa. Furthermore, when del Arco Aguilar (1983)
placed this taxon in T. stenopetala, he reported it as hybridizing with T. canariensis. Because of the difficulty of separating some T. stenopetala subsp. spachiana from T. canariensis, this plant is probably best treated as T. canariensis (spachiana-type). Interestingly, T. stenopetala subsp. microphylla from La Gomera and from El Hierro may not have the same origin (Fig. 3), which would support their independent treatment as advocated by Pitard and Proust (see Gibbs and Dingwall, 1972
).
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Convergent morphologies in the Genisteae
Morphological convergence between unrelated members of the island Genisteae has led to some taxonomic confusion, such as the mistaken synonymization of Genista tenera with Teline osyroides (noted in Gibbs, 1974
). It is also probable that morphological convergence within the "monspessulana clade" resulted in the misclassification of T. stenopetala subsp. spachiana. It is a member of the T. canariensis group but shares a number of characteristics (longer racemose inflorescences, larger leaves and flowers) with the morphologically circumscribed T. stenopetala group. At a higher level, the polyphyletic origin of Teline suggests that a number of the characters used to delimit the genus are convergent (e.g., strophiolate seeds and trifoliolate leaves). In the predominantly unifoliolate Genista sensu stricto, reversals to trifoliolate leaves may have occurred several times (e.g., the trifoliolate G. clavata in this analysis). Development of the seed aril appears to have independent origins in Cytisus and Genista and may also have independent origins in Teline. However, G. segonnei, which is both trifoliolate and possesses strophiolate (rim-aril) seeds, is morphologically similar to Teline (Maire, 1987
), and constraining Teline to be monophyletic with the inclusion of G. segonnei does not require a significant increase in tree length (Table 3). Thus, there is a possibly monophyletic Teline + G. segonnei group which may justify having a section Teline within Genista.
Hybridization and species boundaries
The facility with which island species hybridize when ecological barriers are removed has been addressed for a number of different plant groups (Francisco-Ortega et al., 2000)
. The introduction of several Teline species to North America provides a useful comparison to ecological behavior in the native range. It is notable that the one species reported as "a noxious weed" in California (McClintock, 1993
), T. monspessulana, is the only widespread species within the genus' native distribution. Particularly revealing is the information on interspecific hybridization in California (McClintock, 1993
). Five species of Teline have been introduced into cultivation in California and have become naturalized. Four of these introductions are members of the monspessulana clade, among which hybrids between T. canariensis, T. monspessulana, and T. stenopetala are recorded as "common." Hybrids are also known from Tenerife (and possibly Gran Canaria; Suárez Rodgríguez, 1991
) between T. canariensis and T. stenopetala, where the latter species is not native but cultivated. In contrast, T. linifolia, also naturalized in California, has not been reported forming hybrids with any of the monspessulana clade, and hybrids do not occur between the two Teline clades where these are sympatric in their native distributions. Also unrecorded are hybrids within the linifolia clade. However, contact between native species, which is frequent in the monspessulana clade, does not occur in the linifolia clade and no breeding experiments have been conducted to provide further data. These patterns of hybridization reflect the phylogenetic division in Teline. Further work is required to determine if hybridization in the monspessulana clade in the Canary Islands is contributing to genetic erosion via introgression and assimilation, as has been suggested for other groups (Francisco-Ortega et al., 2000)
.
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FOOTNOTES |
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5 Author for reprint requests, current address: CSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia (diana.percy{at}csiro.au
)
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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