A Revision of Lebeckia Sect. Lebeckia: the L
Total Page：16
File Type：pdf, Size：1020Kb
Available online at www.sciencedirect.com South African Journal of Botany 75 (2009) 83–96 www.elsevier.com/locate/sajb A revision of Lebeckia sect. Lebeckia: The L. pauciflora and L. wrightii groups (Fabaceae, Crotalarieae) ⁎ M.M. le Roux, B-E. van Wyk Department of Botany and Plant Biotechnology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa Received 19 May 2008; received in revised form 30 July 2008; accepted 1 August 2008 Abstract All 14 species of the type section of the genus Lebeckia Thunb. are endemic to the Cape Floristic Region and are easily recognized by their phyllodinous, acicular (needle-shaped) leaves. Ten of the 14 species, comprising the L. sepiaria and L. plukenetiana groups, have already been revised. The last two groups are formally treated in this paper: 1. the L. pauciflora group (two virgate perennials with terete to semi-terete, stipitate fruits) and 2. the L. wrightii group (two trailing fireweeds with flat, sessile fruits). One of these, L. uniflora B-E.van Wyk and M.M.le Roux sp. nov., is here described as new. The new species was previously confused with L. wrightii (Harv.) Bolus but differs in the single-flowered inflorescences, larger flowers and black seeds. The nomenclature, typification, morphological and diagnostic characters are presented as well as distribution maps. A comprehensive key to all 14 species of section Lebeckia is provided. © 2008 SAAB. Published by Elsevier B.V. All rights reserved. Keywords: Cape Floristic Region; Crotalarieae; Fabaceae; Fireweeds; Lebeckia section Lebeckia; Lebeckia uniflora; Revision 1. Introduction Section Lebeckia includes 14 species that are nearly endemic to the Cape Floristic Region (Fynbos and Renosterveld Biomes) Lebeckia Thunb. is the last remaining genus of the tribe with only one species, L. ambigua E.Mey., also occurring in the Crotalarieae that has not been taxonomically revised in recent Namaqualand coastal area (Le Roux and Van Wyk, 2008). years (Harvey, 1862). The genus consists of some 33 species L. section Lebeckia is divided into four informal taxonomic that are endemic to the western parts of southern Africa. groups, mainly based on fruit morphology and habit: 1. The Recent molecular studies have shown that there are four L. sepiaria group – four species, all with sessile, terete or semi- major lineages within the tribe Crotalarieae (Benth.) Hutch. terete fruits and a virgate habit; 2. The L. plukenetiana group – six (Boatwright et al., in press). The genus Lebeckia is placed species, all with stipitate, flat fruits and a prostrate habit; 3. The within the “Cape group”, which includes the genera Aspalathus L. pauciflora group – both species have stipitate, semi-terete to L., Lebeckia, Rafnia Thunb. and Wiborgia Thunb. Lebeckia is terete fruits and a virgate habit; and 4. The L. wrightii group – two not monophyletic and is divided into several small groups. fireweeds, with sessile, flat fruits and stipules (Le Roux and Van Combined molecular and morphological analyses showed the Wyk, 2007; Le Roux and Van Wyk, 2008). type section of the genus, L. sect. Lebeckia, to be monophyletic The L. pauciflora group and the L. wrightii group are revised (Le Roux, 2006). This is supported by four apomorphies, here. One species from the L. wrightii group is described as new, namely the suffrutescent habit, acicular leaves that are often namely L. uniflora B-E.van Wyk and M.M.le Roux sp. nov. articulated near the middle, a 5+5 anther arrangement, and rugose seeds (Le Roux, 2006; Le Roux and Van Wyk, 2007). 2. Materials and methods ⁎ Corresponding author. Herbarium specimens obtained from BOL, JRAU, NBG, P, E-mail address: [email protected] (B.-E. van Wyk). PRE, S and SAM were studied, as well as photographs of 0254-6299/$ - see front matter © 2008 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2008.08.002 84 M.M. le Roux, B.-E. van Wyk / South African Journal of Botany 75 (2009) 83–96 specimens from BM and K. Morphological variation was reach heights of up to 0.35 m and 0.8 m, respectively (Fig. 1a,b). studied on several field trips. Illustrations were prepared using a Plants resprout and flower profusely after fire but the WILD M3Z stereomicroscope with a camera lucida attachment. inflorescences often become sparse and few-flowered in the Specimens of those species that showed geographical variation years following a fire. The Vanrhynsdorp or typical form of were sorted into the following regional forms: L. pauciflora: L. pauciflora may reach 1.0 m, but the Langkloof form is Vanrhynsdorp or typical form, Montagu form (similar to typical somewhat smaller (up to 0.6 m). form but habit smaller, inflorescences shorter), Langkloof form Stipules are commonly reduced in the Crotalarieae, and (habit small, leaves not articulated, inflorescences short); generally absent in section Lebeckia (Van Wyk and Schutte, L. wrightii: Cape Town or typical form, Caledon form (similar 1988; Le Roux and Van Wyk, 2007), but they are uniquely to typical form). present in L. uniflora and L. wrightii (Van Wyk and Schutte, 1989). The stipules are small, narrowly lanceolate and 2–5mm 3. Results and discussion long. Field observations have shown that stipules are absent from the lower leaves of seedlings, but gradually appear along 3.1. Morphology the upper nodes, suggesting that the presence of stipules represents a reversal to an ancestral state in these two highly With the exception of L. uniflora and L. wrightii, all species specialized species. of L. section Lebeckia are perennial suffrutices. These two TheleavesofthespeciesinsectionLebeckia are glaucous species are fireweeds – annuals or at most short-lived perennials and glabrous in all the species except L. uniflora and that rapidly grow and mature only in the immediate post-fire L. wrightii, where they are minutely pubescent. Leaf length phase of fynbos and disappear soon thereafter (Fig. 1c,d). anddensitywerestudiedindetailandwasfoundtobe L. grandiflora and L. pauciflora are virgate suffrutices with inconclusive and of limited diagnostic value (Le Roux, multiple stems spreading from a woody, persistent base and 2006). Fig. 1. Growth form (habit) and fruit shape in the four species of the Lebeckia pauciflora and L. wrightii groups: (a) L. grandiflora (Rooi Els or typical form), [Esterhuysen 14102, (P)]); (b) L. pauciflora (Vanrhynsdorp or typical form, photos taken at Algeria Forest Station); (c) L. uniflora (Caledon or typical form) [Boucher 1878, (NBG)]; (d) L. wrightii (Caledon form), photo taken in Kogelberg Nature Reserve; Photographers: B-E. van Wyk and J.S. Boatwright. M.M. le Roux, B.-E. van Wyk / South African Journal of Botany 75 (2009) 83–96 85 Fig. 2. Diagrams of inflorescence structure and relative flower size in the Lebeckia pauciflora and L. wrightii groups: (a) L. grandiflora;(b)L. pauciflora;(c)L. uniflora; (d) L. wrightii. Scale bar: 10 mm. Some species in section Lebeckia have a joint or articulation Inflorescences of the species in section Lebeckia are usually near the middle of the leaf and its presence or absence is useful densely multi-flowered (up to 95 flowers), terminal racemes for diagnostic purposes. An articulation is invariably present in (Le Roux and Van Wyk, 2007), but those in the L. pauciflora L. grandiflora; always absent in L. uniflora and L. wrightii; and and L. wrightii groups are fewer flowered (Fig. 2). L. grandiflora either absent or present in L. pauciflora, depending on the usually has up to 16 flowers per inflorescence and L. pauciflora location. Northern and southern populations of this species up to 34 flowers. L. wrightii has shorter inflorescences with up to (Vanrhynsdorp or typical form) and Montagu form have the five flowers at most, while L. uniflora typically has a single articulation present but not the eastern populations (Langkloof flower (very rarely two or three) per inflorescence (Fig. 2). form) (see later). If the articulation is absent, the leaves are Lateral branches may rarely occur at the base of the slightly shorter than when it is articulated. inflorescences of L. pauciflora and L. wrightii, while the Fig. 3. Calyces of the Lebeckia pauciflora and L. wrightii groups (calyces are opened out with the upper lobes to the left): (a) L. grandiflora;(b)L. pauciflora;(c)L. uniflora; (d) L. wrightii. Vouchers: (a) from Esterhuysen 14102 (P); (b1) Fourcade 3117 (BOL); (b2) Hanekom 3189 (NBG); (b3) Fourcade 1707 (BOL); (c1) Boucher 1878 (NBG); (c2) Stokoe 964 (BOL); (d1) Esterhuysen 31726 (BOL); (d2) Boucher 1879 (NBG); (d3) Compton s.n. sub. BOL 32416 (BOL).Scalebar:1mm.(candddrawnbyB-E.van Wyk). Scale bar: 1 mm. 86 M.M. le Roux, B.-E. van Wyk / South African Journal of Botany 75 (2009) 83–96 inflorescences of L. grandiflora and L. uniflora are invariably flower size. A unique character within these two groups is the unbranched. helically coiled keel, found in L. pauciflora, L. uniflora and Flower size is of some diagnostic value (Fig. 2). L. wrightii L. wrightii (visible in Fig. 1). It would be worthwhile to has small flowers (up to 8 mm long), whereas L. grandiflora, examine fresh flowers of L. grandiflora for the possible L. pauciflora and L. uniflora have larger flowers (up to 15 mm presence of at least some degree of coiling in this seemingly long). close relative of L. pauciflora. Keel petals are usually rostrate The bracts and bracteoles are simple and sessile in all the (more so in L. pauciflora, L. uniflora and L. wrightii than in species of section Lebeckia. L. uniflora and L. wrightii are L. grandiflora), with ± obtuse apices. unique in section Lebeckia in having minutely pubescent bracts The anthers in section Lebeckia are differentiated into five and bracteoles. Bracts are attached at the base of the pedicel and long, basifixed anthers alternating with five shorter, dorsifixed, usually have a median vein.