A Phylogenetic Study of Echidnopsis Hook. F. (Apocynaceae- Asclepiadoideae) - Taxonomic Implications and the Colonization of the Socotran Archipelago
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Pl. Syst. Evol. 265: 71–86 (2007) Plant Systematics DOI 10.1007/s00606-007-0516-3 and Evolution Printed in The Netherlands A phylogenetic study of Echidnopsis Hook. f. (Apocynaceae- Asclepiadoideae) - taxonomic implications and the colonization of the Socotran archipelago M. Thiv1 and U. Meve2 1Institute of Systematic Botany, University of Zurich, Switzerland 2Lehrstuhl fu¨r Pflanzensystematik, Universita¨t Bayreuth, Germany Received May 9, 2006; accepted January 5, 2007 Published online: April 11, 2007 Ó Springer-Verlag 2007 Abstract. We investigated the phylogeny, taxonomy clear latex, a lack of apical anther appendages and biogeography of the Eritreo-Arabian genus and erect pollinia with pellucid margins (cf. Echidnopsis Hook. f. (Apocynaceae-Asclepiadoi- Meve and Liede 2004). Within this tribe, the deae). Phylogenetic reconstructions based on nrITS genus Echidnopsis is part of subtribe Stapelii- sequence data were obtained using maximum nae G. Don, to which Brachystelma Sims and likelihood and parsimony analyses. The results Ceropegia L. also belong. The stapeliads, or reveal two weakly supported clades, each with a ‘‘carrion flowers’’, are the most speciose group mix of African and Arabian taxa, including the genus Rhytidocaulon, and with four Socotran in the tribe, accounting for ca. 400 species in 38 species forming a subclade of their own. Rather genera of predominantly African, Arabian and than a vicariance origin of these island elements, Indian distribution (Albers and Meve 2002). In our data suggest a single dispersal event from a stapeliad phylogeny based on nuclear and eastern Africa. Echidnopsis thus parallels biogeo- plastid DNA data, Echidnopsis has been shown graphic patterns found for other Socotran endemic to be closely related to Rhytidocaulon P.R.O. plants. Our revised taxonomy recognizes 28 species Bally and Caralluma R. Br. (Meve and Liede and 4 subspecies in the genus. Two new combina- 2002). Plants of Echidnopsis bear small flowers tions, E. planiflora subsp. chrysantha and E. sharpei on creeping succulent stems which are many- subsp. bavazzani are proposed. angled, ca. 1–2 cm in diameter and form dense clusters or mats. They grow on sand or loam, Key words: Biogeography, Echidnopsis, morphology, often covered by bushes, in sand pouches on nrITS, phylogeny, Socotra, taxonomy. rocks, or creeping along rock fissures, shel- tered by rocks or uncovered. Echidnopsis thus exhibits a typical behaviour of stapeliads, Introduction especially for such small-stemmed species with Echidnopsis Hook. f. belongs to the Old World procumbent-ascending growth (cf. Albers et al. tribe Ceropegieae Decne. ex Orb. (Apocynaceae- 1989). Echidnopsis is a medium-sized genus Asclepiadoideae), which is characterized by comprising 45 decribed species of which 28 72 M. Thiv and U. Meve: Phylogenetic study of Echidnopsis plus four subspecies are accepted here Marsdenia R. Br., Sarcostemma R. Br., and (Table 1). The first complete and comprehen- Vincetoxicum Wolf. With five endemic species sive revisions of Echidnopsis were published by Echidnopsis Hook. f., however, represents the Bruyns (1988) and Plowes (1993). These revi- largest Asclepiadoideae taxon on Socotra sions represent rather extreme taxonomic con- (Bruyns 2004). cepts, but while Bruyns favoured a rather In the present paper we focus on three generous lumping and the establishment of main goals: 1) To reconstruct the phylogeny of infraspecific categories, Plowes splitted every Echidnopsis using sequence data of the nuclear morphologically discernable element into a full internal transcribed spacer (nrITS; Baldwin species. Mu¨ller and Albers (2002) offered a et al. 1995, Alvarez and Wendel 2003) 2) We compromise between these revisions, adopting address the taxonomy of the genus Echidnop- some necessary corrections of Bruyns’ revision sis, by evaluating whether existing infrageneric pointed out by Plowes (1993), but without classifications are supported by molecular accepting his many seemingly superfluous new phylogenetic data and by defining this concept taxa. again. Therefore, we focus on species com- The present distribution of Echidnopsis plexes particularly exposed to different taxo- from Tanzania to Oman adheres closely to nomic views in the past, such as E. sharpei/ Takhtajan’s (1986) Eritreo-Arabian Subregion E. repens, E. scutellata/E. planiflora, and E. and the Somali-Masai regional centre of watsonii/E. radians, as well as on the question endemism of White (1983). Takhtajan’s subre- whether E. malum deserves to be recognized as gion covers large parts of north-eastern Africa, a genus separate from Pseudopectinaria Lavr- southern Arabia and the Socotran archipelago. anos, one of the most disputed problems in These three areas equate to the three Provinces Echidnopsis taxonomy (Bruyns 1988, Plowes of this subregion recognised by Takhtajan, the 1993, Lavranos 2006) 3) We investigate the Somalo-Ethiopian, South Arabian and Soco- biogeography of Echidnopsis in the Eritreo- tran Provinces. The vast majority of species Arabian Subregion, focussing on the question can be exclusively attributed to one of its three of the geographic origins of the Socotran floristic provinces (Table 2). The entire region endemics and whether the archipelago was is generally very rich in asclepiadaceous taxa, colonized through a single invasion event and but with eastern and southern Africa as the subsequent radiation or if multiple stochastic uncontested centre of diversity. Whereas some colonization events occurred. taxa occur in both Africa and Arabia (e.g. Kanahia R. Br., Huernia R. Br., Glossonema Materials and methods Decne., Duvalia sulcata N.E. Br., Ceropegia variegata Decne., Edithcolea grandis N.E. Br., Taxa. The material used in this study, including Monolluma socotrana (Balf. F.) Meve & Liede, voucher specimen, author name, donor or collector Pentatropis nivalis (J.F. Gmel.) D.V. Field of material, area of distribution and EMBL J.R.I. Wood), a considerable number occurs number is summarized in Table 2. The ingroup only in the Arabian Peninsula (cf. Miller and comprises 32 accessions of Echidnopsis in 26 Morris 1988, Miller and Cope 1996, Wood different taxa according to the verified taxonomy of Echidnopsis as proposed in this paper (Tables 1, 1997, Collenette 2000). In contrast, the island 2). Due to the lack of living material available to of Socotra is home to fewer Asclepiadoideae us, the Socotran E. milleri and E. virchowii were not than the African and Arabian mainland investigated. Material of E. seibanica was available, (cf. Mies 1998, 2001). Among the Socotran however, sequencing of nrITS failed. Caralluma endemics are the genus Duvaliandra M.G. subulata, C. priogonium, Monolluma socotrana, Gilbert (with two species if Socotrella Bruyns Rhytidocaulon macrolobum and R. fulleri were used is included), a single species each in the genera as outgroups (Table 2). Table 1. Taxonomic concepts in Echidnopsis (taxa here accepted are printed in bold), and chromosome numbers (new counts marked by *, M. Thiv and U. Meve: Phylogenetic study of otherwise taken from Albers and Meve 2001) Taxon Bruyns 1988 Plowes 1993 Thiv and Meve, Chromosome number this paper (2n) E. angustiloba E.A. E. angustiloba E. angustiloba E. angustiloba 22 Bruce & P.R.O Bally E. archeri P.R.O. Bally E. archeri E. archeri E. archeri 22 E. ballyi (Marn.-Lapost.) E. ballyi E. ballyi E. ballyi 22 P.R.O. Bally E. bavazzani Lavranos = E. sharpei E. bavazzani E. sharpei subsp. 22* bavazzani (voucher:Lavranos 24979) E. bentii N.E. Br. ex Hook. f. - insuff. known species E. bentii E. bentii 22* (voucher: - (Bruyns 2004: E. bentii) Wolf s.n., UBT) E. bihendulensis P.R.O. Bally E. bihendulensis E. bihendulensis E. bihendulensis 22* (voucher: Specks s.n.) Echidnopsis E. cereiformis Hook. f. E. cereiformis E. cereiformis E. cereiformis 22 E. chrysantha Lavranos = E. scutellata subsp. planiflora E. chrysantha E. planiflora subsp. 44 chrysantha E. chrysantha var. filipes E. scutellata subsp. planiflora E. chrysantha = E. planiflora subsp. 22 Lavranos subsp. filipes chrysantha (Lavranos) Plowes E. ciliata P.R.O. Bally E. sharpei subsp. ciliata E. ciliata E. ciliata 22 (P.R.O. Bally) Bruyns E. dammanniana Spreng. E. dammanniana E. dammanniana E. dammanniana 22 E. ericiflora Lavranos E. ericiflora E. ericiflora E. ericiflora 22 E. fartaqensis McCoy — (descr. 2003) — (descr. 2003) = E. globosa 22* (voucher: & Orlando Lavranos & Mies 31326, UBT) E. flavicorona Plowes Type specimen incl. in E. flavicorona = E. planiflora subsp. – E. scutellata subsp. planiflora planiflora E. globosa Thulin –- (descr. 1995) — (descr. 1995) E. globosa 22 & Hjertson E. hirsuta Plowes Type specimen incl. in E. hirsuta = E. planiflora subsp. – E. scutellata subsp. planiflora planiflora E. inconspicua Bruyns — (descr. in 2005) — (descr. in 2005) E. inconspicua – E. insularis Lavranos E. insularis E. insularis E. insularis – 73 Table 1. (Continued) 74 M. Thiv and U. Meve: Phylogenetic study of Taxon Bruyns 1988 Plowes 1993 Thiv and Meve, Chromosome number this paper (2n) E. jacksonii P.R.O. = E. urceolata E. jacksonii - insuff. known taxon - – Bally ex Plowes E. lavraniana Plowes Type specimen incl. E. lavraniana = E. sharpei subsp. 22 in E. sharpei bavazzani E. leachii Lavranos E. leachii E. leachii E. leachii 22 E. malum (Lavranos) E. malum Pseudopectinaria malum E. malum 22 Bruyns ” Pseudopectinaria malum E. mariae Lavranos = E. scutellata subsp. E. mariae = E. scutellata subsp. 22 australis Bruyns australis E. mijerteina Lavranos E. mijertina E. mijertina var. E. mijertina 22 mijertina E. mijerteina var. marchandi = E. mijertina E. mijertina var. = E. mijertina 22 Lavranos marchandii E. milleri Lavranos – (descr. in 1993) – (descr. in 1993) E. milleri – E. modesta P.R.O. = E. watsonii E. modesta = E. radians – Bally ex Plowes E. montana (R.A. Dyer E. montana E. montana E. montana 22 & E.A. Bruce) P.R.O. Bally E. nubica N.E. Br. = E. cereiformis E. nubica = E. cereiformis 22 E. oviflora McCoy – (descr. in 2003) – (descr. in 2003) = E. leachii (22*, voucher: Specks 1264, UBT) E. planiflora P.R.O. Bally E. scutellata subsp. planiflora E. planiflora E. planiflora subsp. 22 / 44 (P.R.O. Bally) Bruyns planiflora E. plowesiana Orlando – (descr. in 2004) – (descr. in 2004) = E.