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Systematics |
2Institute of Botany, University of Vienna, Austria; 3Royal Botanic Garden Edinburgh, Scotland, UK; 4Conservatoire et Jardin Botaniques de la Ville de Genève, C.P. 60, CH 1292 Chambésy, Switzerland
Received for publication April 2, 2002. Accepted for publication September 10, 2002.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: Epithematheae • Gesneriaceae • rbcL/atpB spacer • systematic position • trnL-F intron spacer
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Burtt, 1978
; Wang and Pan, 1996
). (2) Though clearly centered in tropical southeast Asia, the geographical range is wide and includes (warm-)temperate China (Whytockia, Rhynchoglossum pro parte), West Africa (one species of Epithema), and even the neotropics (one species of Rhynchoglossum). Epithemateae is indeed the only part of subfamily (subfam.) Cyrtandroideae that reaches America. (3) In view of the diverse and strange morphological patterns it is very difficult to characterize and delimit the tribe.
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; Fritsch, 1893–1894
), Burtt (1963)
filtered out a number of odd genera and classified them into two tribes: Klugieae and Loxonieae. The former contained Rhynchoglossum (including Klugia; Burtt, 1962
), Monophyllaea, Moultonia (now included in Monophyllaea; Burtt, 1978
), and Epithema. The latter contained Loxonia, Stauranthera, Whytockia, and "for want of a better place" Cyrtandromoea. Burtt (1965)
himself later removed Cyrtandromoea from the tribe by transferring it to the family Scrophulariaceae.
In a series of morphological analyses, Weber (1975–1982) showed that the generic affinities run across the two tribes and the separation of Klugieae and Loxonieae no longer appeared tenable. The suggested union into a single tribe (Klugieae) was accepted informally by Burtt (1977)
and later formally by Burtt and Wiehler (1995)
and Burtt (1997)
, who also replaced the tribal name Klugieae written Epithemateae due to priority reasons.
Epithemateae stands as a compact group with Epithema, Loxonia, Monophyllaea, Rhynchoglossum, Stauranthera, Whytockia, and Gyrogyne, another monotypic, and little-known genus later added by Wang (1981)
. Its position within Gesneriaceae, however, has recently become a matter of dispute. It became increasingly apparent that the Epithemateae was not a tribe equivalent to the other tribes of Cyrtandroideae, but was rather juxtaposed to all other Cyrtandroideae. Based on molecular ndhF data, Smith et al. (1997)
even suggested that Epithemateae is sister to all other (including neotropical and austral) Gesneriaceae and considered the group to represent an old and relic assemblage that has evolved and differentiated very early and in isolation from the rest of Gesneriaceae.
In view of the complex morphology of the Epithemateae a broad molecular approach is an appropriate approach to analyze its infra- and intratribal relationships. Chloroplast DNA (cpDNA) sequences such as the rbcL-atpB spacer and the trnL-F intron-spacer regions were used for our present phylogenetic analysis, as these regions were previously found suitable to resolve generic relationships within Gesneriaceae (Samuel, Kiehn, and Pinsker, 1997
; Samuel, Pinsker, and Kiehn, 1997
; Möller et al., 1999
).
The intent of the present study is to contribute to a better knowledge of (a) the position of the Epithemateae within the family Gesneriaceae and (b) the relationships and evolutionary differentiation of the genera included in this group.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Therefore the trees were rooted on members of the Solanaceae that have been shown to be distant enough from Gesneriaceae/Scrophulariaceae (Chase et al., 1993
; Olmstead et al., 1993
; Olmstead and Reeves, 1995
) but close enough to allow unproblematic sequence alignment. Representative members of Scrophulariaceae have been added to illustrate the monophyly of the ingroup taxa of Gesneriaceae included.
Ingroup taxa
With the exception of Gyrogyne, representatives of all genera of Epithemateae could be included in the analysis (See table at http://ajbsupp.botany.org/v90/). Gyrogyne subaequifolia W. T. Wang, the only species of Gyrogyne, could not be investigated due to the lack of adequate material. The species is only known from the type collection, and the isotype available to us did not yield successful DNA extracts.
For establishing the position of the Epithemateae within Gesneriaceae, representatives of all tribes of subfamilies Cyrtandroideae, Coronantherae, and Gesnerioideae were included in the analysis (http://ajbsupp.botany.org/v90/). In a few cases (marked by an asterisk) atpB-rbcL spacer sequences of Samuel, Kiehn, and Pinsker (1997)
and Samuel, Pinsker, and Kiehn (1997)
were used. Voucher specimens are deposited in Edinburgh (E), Vienna (WU) and Genève (G).
DNA extraction, polymerase chain reaction, and sequencing procedures
For DNA extraction fresh leaf material, leaves dried in silica gel (from plants cultivated at the HBV = Hortus Botanicus Viennensis and RBGE = Royal Botanic Garden Edinburgh), or leaves from herbarium specimens were used. The material collected by A. Weber in Peninsular Malaysia was quickly dried with a simple transportable ventilator system and proved to be very suitable for DNA extraction.
DNA extraction was made with DTAB/CTAB after Savolainen et al. (1995)
or Doyle and Doyle (1987)
. Of the several attempts made with DNA extracts of herbarium specimens 
60% gave genuine amplification products in polymerase chain reactions (PCR) (as judged from the fragment length on agarose gels). The atpB primers used were the forward primer "JF31" (TTT CAA GCG TGG AAA CCC CAG) and the reverse primer "JF5" (TAC AGT TGT CCA TGT ACC AG); for manual sequencing also the internal primers "JF9" (GTC TAT GAT TAT AGA CAA TCC) and "JF7" (CCC TAC AAC TCA TGA ATT AAG) were also used (Manen, Natali, and Ehrendorfer, 1994
).
The trnL-F region was PCR amplified using primers "C" and "F" (Taberlet et al., 1991
), amplifying the trnL (UAA) intron and the intergenic spacer between the trnL (UAA) 3' exon and the trnF(GAA)5' exon.
For the atpB spacer region PCR was performed in volumes of 50 µL with the following final concentrations: 1x standard PCR reaction buffer (10 mmol/L Tris-HCl pH 8.3, 50 mmol/L KCl), 2.0 mmol/L MgCl2 (2.5–3.0 mmol/L for herbarium extractions), 0.004% BSA, 0.2 µmol/L of each dNTP, 0.2 µmol/L each primer, and 0.7 units Taq-Polymerase (Boehringer, Ingelheim, Germany). Each sample was subjected to an initial cycle of 5 min denaturation at 95°C, 3 min annealing at 46°C, and 5 min extension at 72°C. Thereafter, 35 cycles, each consisting of a denaturation step of 1 min at 95°C, an annealing step of 1 min at 55°C, and an extension step of 1 min at 72°C followed. A final extension of 10 min at 72°C completed the amplification. The PCR products were purified using a Quiagen QuiaQuick Gel Extraction Kit (Crawley, West Sussex, UK).
Sequencing was performed in the forward and reverse directions. At the beginning of the study T7 polymerase was used manually and later an ABI 377 automated sequencer using a dye terminator cycle-sequencing ready-reaction kit (Perkin Elmer, Applied Biosystems Division, Foster City, California, USA) was used, with 4 µL and later 2 µL Dye Terminator (with equal results) in a total of 10 µL reaction used.
For the trnL-F region, the PCR reaction mixture and PCR cycle parameter, amplicon purification, quantification, and sequencing procedures are described elsewhere (Möller et al., 1999
).
Sequence alignment and phylogenetic analysis
The first unambiguously alignable sequence of the rbcL/atpB spacer was used as sequence boundary at the 5' end. The 3' end was determined by the start of the rbcL coding sequence in comparison with published rbcL sequences of Streptocarpus (GBAN-AF170250). For the trnL-F region, sequence boundaries were determined in comparison to published Nicotiana tabacum sequences (GBAN-Z00044). Obtained sequences were aligned using the CLUSTAL option in the multiple alignment program Sequence NavigatorTM Version 1.0.1 software package (Perkin Elmer, Applied Biosystems Division, Foster City, California, USA), followed by manual optimization. Sequence divergence among taxa was calculated using the DISTANCE MATRIX option in PAUP Version 4.0b8 (Swofford, 2001
). For analyses of sequence data, only combined atpB and trnL-F data of unambiguously alignable positions were used, and gaps (indels) were treated as missing data. Indels were scored as a separate presence/absence character and added to the sequence data matrix in a separate analysis (Wojciechowski et al., 1993
; Oxelman and Lidén, 1995
).
Maximum parsimony (MP) analyses were performed with characters unweighted and unordered. Two search strategies were pursued. The first was a heuristic search with simple addition sequence, tree bisection-reconnection (TBR) and Multrees on. The second consisted of a modified stepwise search method (Soltis and Soltis, 1997
) to optimize the heuristic searches for most parsimonious trees (MPT). In the first round 10 000 replicates of random addition sequence with nearest-neighbour interchanges (NNI) swapping algorithm activated, Multrees and steepest descent deactivated, terminating each replicate after saving not more than two trees of n tree length (the n tree length was established empirically in the first heuristic search). The stored trees were then subjected to TBR swapping algorithm with Multrees and steepest descent on in the second step of this search process. This strategy is designed to efficiently detect multiple islands of MPT that may exist (Maddison, 1991
).
Descriptive tree statistics (consistency index [CI: Kluge and Farris, 1969
], retention index [RI: Farris, 1989
], rescaled consistency index [RC: Swofford, 2001
]) were performed using PAUP. Statistical branch support analyses were performed threefold, as 10 000 replicates of fast jackknifing (JK) with 50% character deletion and as 1000 replicates of heuristic bootstrap (BS) (Felsenstein, 1985
) with TBR swapping on and Multrees off (Spangler and Olmsteadt, 1999
) under PAUP. Decay indices (DI) were derived from AutoDecay 4.0.2 (Eriksson, 1999
) and PAUP on 100 replicates of random addition.
To test for rate heterogeneities in sequence evolution across the matrix, a likelihood ratio test was conducted on a single most parsimonious tree with the highest likelihood value (of the combined data set) (Möller and Cronk, 2001
). The maximum likelihood (ML) model chosen using Modeltest 3.06 (Posada and Crandall, 1998
) was TVM + G. This uses a tranversion model (TVM, variable base frequencies, variable transversions, transitions equal) with gamma-distributed among-site rate variation (G).
To address the high rate heterogeneity across the matrix (in particular, of members of tribe Klugieae) and to investigate their effect on tree topology, additional parsimony analyses (using the same settings as above), either excluding all Epithemateae or on Epithemateae sequences alone, rooted on all outgroups were executed. Any significant deviation in topology of the reduced data sets would indicate problems of long branch attraction associated with high rate heterogeneities (Siddall and Whiting, 1999
).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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.
Phylogenetic analysis
The atpB-rbcL spacer and trnL-F intron-spacer regions were analyzed independently and combined. The phylogenetic analysis of combined atpB-rbcL and trnL-F data plus the alignment gap matrix produced 270 most parsimonious trees of 1641 steps, with a consistency index (CI), a retention index (RI), and a rescaled consistency index (RC) (including uninformative character) of 0.7246, 0.8615, and 0.6242, respectively. The average character change per position was 0.88, indicating a relatively low saturation of base substitution and a low potential of multiple substitutions and reversals obscuring the phylogenetic signal. Jacknife and bootstrap values were between 56 and 100% and 51 and 100%, respectively, and decay indices were between 1 and 103. The atpB-rbcL spacer region plus alignment gap matrix produced 100 700 most parsimonious trees of 728 steps, the trnL-F data plus the alignment gap matrix produced 3863 most parsimonious trees of 898 steps. Jackknife and bootstrap values were between 65% and 100% and 50% and 100%, respectively, for the atpB-rbcL spacer region and between 51% and 100% and 53% and 100%, for the trnL-F data.
Tree topology
The resulting strict consensus tree of 270 most parsimonious trees of combined data sets showed a monophyletic Epithemateae in the combined tree (bootstrap [BS] = 100%; jackknife [JK] = 100%; decay index [DI] = 12) (Fig. 2), sharing 22 synapomorphic character state changes as depicted in one of the resulting trees, which reproduced as phylogram indicating the respective branch lengths (Fig. 3).
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Taxa belonging to subfamilies Gesnerioideae and Coronantheroideae formed a monophyletic clade albeit with low branch support (BS = 68%; JK = 64%; DI = 1) and the latter subfamily unresolved on a basal polytomy with members of the tribes Napeantheae and Beslerieae. The rest of the subfam. Cyrtandroideae (except tribe Epithemateae) formed a well-supported monophyletic group (BS = 100%; JK = 100%; DI = 33), with the European taxa basal (BS = 100%; JK = 99%; DI = 7) followed by African representatives (BS = 92%; JK = 85%; DI = 2). The Asian taxa formed several well-supported clades splitting taxa with straight and twisted capsules (Emarhendia, Rhabdothamnopsis, Paraboea, Trisepalum) (BS = 99%; JK = 97%; DI = 6).
An ML analysis on the combined data set using the parameter settings suggested by Modeltest resulted in an identical tree topology compared to the MP analysis.
Analyzing both data sets individually resulted in similar tree topologies: Epithemateae are well supported (BS = 98%, JK = 93% in atpB-rbcL data and BS = 98%, JK = 89% in trnL-F) in both trees; the position of genera within Epithemateae remain the same. On the infrageneric level differences were found in (1) Stauranthera and Loxonia, for which no resolution was obtained in the atpB-rbcL tree. This is reflected by low support (BS = 68%; JK = 64%) in the combined tree. (2) In Epithema the two Malayan species E. membranaceum and E. saxatile resulted as a sister group to an African E. tenue and Taiwanese E. taiwanense clade in the atpB-rbcL data, whereas in the trnL-F tree E. tenue were basal to the three Asian species. (3) For the Monophyllaea species no resolution could be obtained with atpB-rbcL, but due to the strong signals in trnL-F, good resolution with high support (BS = 100%; JK = 100–99%) could be found in the combined tree (Fig. 2).
Conflicting results occurred further in the position of some of the remaining Cyrtandroideae, above all Aeschynanthus, Cyrtandra, Didymocarpus, and Petrocosmea. In the atpB-rbcL tree subfamilies Coronantheroideae and Gesnerioideae remained unresolved on a basal polytomy; within Gesnerioideae resolution was poor for many species in this data set.
In summary the atpB-rbcL tree showed a much lower resolution than the trnL-F tree. Combining the data sets synergistically improved tree resolution, though the areas of conflicting signals (indicated with arrows in Fig. 2) have also low support in the combined tree.
Rate heterogeneities and "pruned" trees
The likelihood ratio test indicated a significant (P > 0.001) variation in the rate of sequence evolution across the matrix, suggesting that cpDNA of taxa of tribe Epithemateae evolves at a significantly faster rate compared to other taxa.
Removal of Epithemateae taxa from the matrix did not significantly alter the topology of the remaining taxa compared to the full analysis (only the two taxa of subfam. Coronantheroideae were resolved as sister to other New World taxa). Conversely, analyzing Epithemateae alone gave an identical tree topology within the tribe compared to the full analysis. This suggests that the rate heterogeneity has no detrimental effect due to possible long branch attraction.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Phylogenetic position of Epithemateae within Gesneriaceae
There has been conflicting discussion on the systematic and phylogenetic position of Epithemateae within the family Gesneriaceae. After fusion of the tribes Klugieae and Loxonieae, the resulting Epithemateae remained at the same (tribal) rank (Burtt and Wiehler, 1995
). It had, however, already become apparent that the Epithemateae were marked off from the rest of Cyrtandroideae and eventually could be regarded as a subfamily of its own (Burtt, 1977
). In their molecular study of the family, using ndhF cpDNA sequences, Smith et al. (1997)
found that the two members of Epithemateae included in their analysis (Monophyllaea hirticalyx and Rhynchoglossum notonianum) plus Cyrtandromoea (transferred to Scrophulariaceae by Burtt, 1965
) are sister to all other Gesneriaceae. However, no branch support (given as decay index) relevant for this placement was indicated in the phylogenetic tree of Smith et al. (1997)
. This position would be very surprising; because of the pronounced anisocotyly Epithemateae show clear morphological affinities with other Old World Gesneriaceae. However, in a later paper combining morphology, ndhF, and rbcL, Smith (2000
: Fig. 7) found that Epithemateae are sister to the remainder of Cyrtandroideae.
The present results based on combined atpB and trnL-F data confirm this result. In our analysis the Epithemateae form a sister clade to the other paleotropical Gesneriaceae, with good branch support (BS = 88; JK = 85; DI = 3; Fig. 2). As discussed later, its extant genera are probably remnants of a once much larger group, now showing—as compared to other Cyrtandroideae—severe morphological and molecular differences and discontinuities. The branches of Epithemateae are the longest in the molecular tree and, in particular, much longer than in the New World taxa, further supporting this hypothesis. Epithemateae therefore is a small and diverse group that clearly belongs to the paleotropical Gesneriaceae (subfam. Cyrtandroideae) and is well marked off from the rest of the group.
Affinities between the genera of Epithemateae
Here we briefly discuss the relationships, essentially based on the molecular data. An ample account relating to the morphological diversification and complex character evolution will be provided at a later opportunity (A. Weber, unpublished data).
Rhynchoglossum
The genus Rhynchoglossum comprises about ten species. The Asiatic range is from India and Sri Lanka to New Guinea. The three species described from the neotropics (R. azureum, R. grandiflorum, and R. violaceum) are considered to represent a single, variable species, R. azureum (Wiehler, 1983
). The species can be roughly classified into two groups: (1) perennials with large flowers and four stamens (the former genus Klugia) and (2) annuals with small flowers and two stamens.
The three species/five acquisitions available for analysis, R. notonianum (southern India), R. azureum (Mexico to Peru; material from Costa Rica), and R. obliquum (India, southern China, Malay archipelago to New Guinea; material from the Malay peninsula, the Philippines, and Taiwan), cover both groups. These groups are reflected in the phylogram by two clades: R. notonianum and the neotropical R. azureum vs. the three acquisitions of R. obliquum (Fig. 3). The tree thus reflects clearly the morphology and not the geographical pattern, which can be seen as an indication that R. azureum is a recent introduction to the Neotropics and that it does not represent an ancient relict. The low sequence divergence of 0.7% between this species and R. notonianum is further evidence.
The sister position of Rhynchoglossum to the remaining Epithemateae is in accordance with the many and strong morphological differences (e.g., alternate, strongly asymmetrical leaves, terminal inflorescences in the form of unilateral racemes, enlarged lower lip of corolla; for details see Weber, 1978a
, b
, c
). Nonetheless, the juxtaposition comes as a slight surprise. The genus has many special characters in common with the other Epithemateae, except the Monophyllaea/Whytockia pair. Therefore, our expectation was that the hiatus would be between Monophyllaea/Whytockia and the other Epithemateae including Rhynchoglossum. But according to the present data, this is not the case.
Epithema
The genus includes more than 20 species (B.L. Burtt and O. Hilliard, Edinburgh, unpublished data) and has a very wide geographical distribution: West Africa (E. tenue) and from northern India, southern China, and Taiwan over the Malay archipelago to New Guinea and the Solomon Islands. Four species (the African E. tenue, two Malayan species, and one Taiwanese species) were included in the analysis.
The species show remarkably little morphological variation, with a uniform and unique basic pattern: the strongly unequal pair of cotyledons is followed by a solitary leaf. Then one or two pairs of isophyllous leaves follow. The solitary and the paired leaves produce several axillary inflorescences in the form of a strongly condensed pair-flowered cyme, which is enclosed by a cucullate bract. Weber (1976a
, b
, 1988
) showed that this unusual pattern is obviously derived from anisophylly, including the inflorescences, which are apparently reduced forms of formerly more elaborate alternicladic thyrses.
The curious and unique morphology did not allow a clear statement about the relationships with other genera. Weber (1976a
, b
) denied a closer relationship with Monophyllaea (superficial similarity in the much enlarged macrocotyledon and inflorescences) and suggested a somewhat closer relationship with Loxonia and Stauranthera (Weber, 1977b
). The molecular data show that Epithema has a rather isolated position, but is clearly nested within Epithemateae.
Surprisingly, the African E. tenue is placed basal to the Asiatic species. This is suggestive of a relict status of this species in Africa from a wider distribution of the genus in the past, similar to Saintpaulia (Möller and Cronk, 1997
).
Loxonia and Stauranthera
Loxonia is a genus of three species, whose distribution ranges from the Mentawai Islands over Sumatra to Borneo and Java (Weber, 1977a
). Stauranthera includes about five species with a range from northeastern India and southern China southwards over the Malay archipelago to New Guinea (A. Weber, unpublished data). Only a single species of each genus could be included in the molecular analysis.
In both genera the plant architecture is very similar (strong anisophylly, sympodial structure of the flowering region, terminal inflorescences in the form of alternicladic thyrses; Weber, 1977b
), but the flowers look very different. Nonetheless, Weber (1977b)
suggested that the two genera Loxonia and Stauranthera are somewhat closely related. This is now corroborated by the molecular data, though the support is not very high.
Gyrogyne
Due to the lack of adequate material, the seventh genus of Epithemateae, Gyrogyne W.T. Wang, could not be included in the analysis (see above, Materials and methods: Ingroup taxa). Its only species, G. subaequifolia W.T. Wang, is known only from the type collection and is probably extinct in the wild (Y. Z. Wang, Beijing, personal communication). W. T. Wang (1981)
included it in Epithemateae and placed it next to Stauranthera on account of the plicate calyx very similar to and characteristic of that genus. In contrast to Stauranthera, which is strongly anisophyllous, the leaves of Gyrogyne are nearly equal, which is seen as the ancestral condition by Wang (1981)
. No further information can be added here.
Whytockia and Monophyllaea
Whytockia is a small genus that has a more northerly and definitely extratropical distribution (southern China, Taiwan). Three species have been recognized in the revision of Weber (1982a)
, but recently a few more have been discovered (Wang, 1995
; Wang and Li, 1997
). One species, W. tsiangiana, was included in the analysis. Monophyllaea is a much larger genus and essentially confined to the ever-wet tropics from southern Thailand and the Philippines to Sumatra and Java eastwards to New Guinea. In the present analysis four species could be included: M. horsfieldii, M. hirticalyx, M. elongata (all Malay peninsula and belonging to subgenus [subg.] Monophyllaea), and M. glauca (Borneo, subg. Moultonia).
The species of Whytockia are uniform in gross morphology and display the simplest architecture in the present alliance: the shoots bear distinctly anisophyllous leaf pairs. Lateral shoots, in the form of pair-flowered cymes, emerge only from the axils of the plus leaves. The cymes are loosely branched and comprise a low to moderate number of (partly still large) flowers. In the simple anisophyllous shoot and inflorescence construction Whytockia conforms perfectly to a morphological archetype of Epithemateae, and in fact we adhere to the opinion that this genus has preserved the ancient construction of the hypothetical ancestor of that group. Weber (1976a)
showed that the unifoliate architecture of Monophyllaea can be well derived from the pattern found in Whytockia.
It was suggested that the relationship between these two genera must be particularly close (Weber, 1975a
, b
, 1976a
, b
). There are several uncommon floral characters (imbricate-descending aestivation of sepals; secretory canals in the sepals; chalk-secreting glands on the inner side of the sepals; descending ["antirrhinoid"] petal aestivation; bilocular ovary) that bind the two genera tightly together. The prediction of a close relationship is now considerably substantiated by the molecular data: Whytockia and Monophyllaea form a distinct clade (BS = 100%; JK = 100%; DI = 13). The phylogenetic relation of the two genera is not obvious from the molecular tree. Morphology suggests that Whytockia is the ancestral type. More recently, the chromosome numbers of Whytockia (x = 9) and Monophyllaea (x = 10, 11, 12) became known (Kiehn and Weber, 1998
; Wang, Gu, and Hong, 1998
). These numbers can be brought into a line of ascending dysploidy, in which Whytockia marks the starting point.
Though we have tried to analyze a greater number of Monophyllaea species from both subgenera (from herbarium material) we succeeded only in three species of subg. Monophyllaea and one from subg. Moultonia. The distal position of the latter is in accordance with the view that subg. Moultonia is more advanced than subg. Monophyllaea. No other statements about the relationships within Monophyllaea can be made at present.
Phylogenetic relationships among other alliances
The present analysis includes 56 species of Gesneriaceae representing 41 out of 147 genera. This seems adequate for evaluating the position of Epithemateae within the family and generic relationships within tribe Epithemateae, but is not enough for making far-reaching conclusions about the systematics of the family as a whole. Nonetheless, a few brief notes can be made in advance of a much broader analysis, which is currently under preparation.
1) The south-hemispherical genera Lenbrassia and Sarmienta, recently placed (together with Depanthus, Coronanthera, Mitraria, Negria, and Rhabdothamnus) in a separate subfamily by Wiehler (1983)
, form a clade that is closely associated with the neotropical Gesneriads. This has also been found by Smith and Caroll (1997)
and Smith and Atkinson (1998)
; though the status of the alliance must be questioned.
2) The placement of the neotropical genera is in good accordance with the current systematic subdivision of neotropical Gesneriaceae (subfam. Gesnerioideae) into morphologically defined sections (Wiehler, 1983
) and the molecular data of Smith et al. (1997)
and Zimmer et al. (2002)
. The suggestion of Smith et al. (1997)
to add a sixth tribe (section Sinningieae) to the five tribes recognized by Wiehler (for the accomodation of Sinningia, Paliavana, and Vanhouttea) can be supported.
3) The paleotropical Gesneriaceae (subfam. Cyrtandroideae) consist of two blocks: the Epithemateae and the ill-resolved remaining paleotropical Gesneriaceae. In the latter, a subdivision into the three tribes as recognized by Burtt (1963
: Cyrtandreae, Trichosporeae, Didymocarpeae) cannot be observed: Cyrtandreae (Cyrtandra) and Trichosporeae (Agalmyla, Aeschynanthus) are nested within Didymocarpeae.
4) At the present state, three alliances of different geographical distribution become apparent: (a) a European group (Haberlea, Ramonda), morphologically defined by septicidal dehiscence of the capsules, (b) an African group (Streptocarpus, Saintpaulia nested in Streptocarpus; for details see Möller and Cronk, 1997
, 2001
), and (c) a large Asiatic group. In the latter group, taxa from tropical southeastern Asia are over-represented and taxa from subtropical and temperate Asia (Rhabdothamnopsis, Petrocosmea, Primulina, Chiritopsis) are under-represented. A better representation of extra-tropical Asian taxa will provide a more differentiated and certainly more complicated picture.
5) The recent split of Didymocarpus (in Asia) into Didymocarpus sensu stricto (s.s.) and Henckelia (Weber and Burtt, 1998
) is supported by the different position of the respective species. Trisepalum fits well with Paraboea.
Conclusions
The results obtained by the molecular analysis are in fair agreement with the morphological data and taxonomic expectations. Several predictions at the generic level are clearly supported by the molecular data: (1) Whytockia and Monophyllaea, despite their outward dissimilarity, are closely related; (2) the anisophyllous-anthocladic Stauranthera and Loxonia, despite their rather different flowers, are closely related; (3) the morphologically isolated Epithema (to be interpreted as derived from anisophyllous ancestors) is allied to Loxonia and Stauranthera.
Especially remarkable is the confirmation that the genera Whytockia and Monophyllaea are closely related. This supports also the view that Monophyllaea evolved on the Asiatic continent (Weber, 1982a, b
). The great species number and the widespread occurrence of Monophyllaea in the humid tropics can be interpreted as an invasion from the continental subtropics and an explosive speciation in the ever-wet tropics. A south- and eastwards migration (Malay Peninsula and Sumatra: 8 species), with highest diversification in Borneo (15 species), over Celebes (1 species) and the Moluccas (2 species), and finally reaching New Guinea (3 species), appears more plausible than an eastern (New Guinea) origin and westward spread (the "tentative" view of Burtt, 1978
). This is consistent with the view that subg. Moultonia evolved later than subg. Monophyllaea, namely when the genus had already reached Sumatra and Borneo. Both subgenera then spread to New Guinea (one species of subg. Monophyllaea, two of subg. Moultonia).
With regard to characters, some prominent floral characters of Whytockia and Monophyllaea deserve discussion: the imbricate sepal aestivation, the presence of chalk glands on the inner side, the presence of secretory canals, the antirrhinoid corolla aestivation, and the bilocular ovary. A key to the genera of Epithemateae would probably start with this character complex to separate Whytockia/Monophyllaea from the remainder of Epithemateae. In contrast, the molecular tree separates Rhynchoglossum first from the rest of Epithemateae. However, upon closer inspection of these floral characters, it is apparent that all represent synapomorphies (binding the two genera morphologically together), and it is well conceivable that they evolved later than the basal split.
The remaining point of discussion is the position and evolutionary state of Rhynchoglossum. Weber (1978a, p. 41)
stated that this genus is closer allied to Epithema, Loxonia, and Stauranthera rather than to Whytockia and Monophyllaea and that the closest relative could be Loxonia. Simultaneously, however, it was expressed that Rhynchoglossum cannot be directly derived from Loxonia as the formal morphological series of inflorescence structure would suggest. The molecular tree now suggests that Rhynchoglossum stands apart from all other Epithemateae. This deserves interpretation. In our opinion, this does not mean that Rhynchoglossum is the most primitive genus of the whole alliance from which all other genera derived. Without a doubt, Rhynchoglossum has a very complex morphological structure and is highly derived. This side position rather seems to indicate that Rhynchoglossum (or more likely its ancestors) split off very early from the other taxa then existing and that there was a long period of time available for the evolution of a highly elaborate morphological pattern in isolation.
The reconstruction of the evolutionary changes in morphology of Epithemateae is a promising subject, but would go beyond the limits of the present paper. A treatment with characterization of a hypothetical ancestor of Epithemateae, reconstruction of character evolution, phytogeographical considerations, a new taxonomic circumscription, and keys to the taxa of Epithemateae will be provided in due course.
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FOOTNOTES |
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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