Geissorhiza Melanthera Sp., Nov. (Iridaceae: Crocoideae) from The
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South African Journal of Botany 87 (2013) 22–24 Contents lists available at SciVerse ScienceDirect South African Journal of Botany journal homepage: www.elsevier.com/locate/sajb Short communication Geissorhiza melanthera sp., nov. (Iridaceae: Crocoideae) from the southern African winter rainfall region with comments on its pollination by the bee-fly Megapalpus capensis (Bombyliidae) P. Goldblatt b,⁎, J.C. Manning a,b a Compton Herbarium, South African National Biodiversity Institute, Private Bag X7, 7735 Claremont, Cape Town, South Africa b Research Centre for Plant Growth and Development, School of Life Sciences, University of KwaZulu-Natal, Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa article info abstract Article history: The new species Geissorhiza melanthera is a member of sect. Engysiphon of subgenus Weihea and is distinguished Received 11 January 2013 by its beige-yellow flowers with the bases of the tepals and throat of the perianth tube bright red. The unscented Received in revised form 4 March 2013 flowers are zygomorphic with unilateral and declinate stamens and style extended horizontally. Its most striking Accepted 5 March 2013 feature is the black anthers with latrorse dehiscence and a portion of the connective visible on the adaxial surface. Available online 9 April 2013 Field observations on two separate days showed the only visitor to be the bee-fly Megapalpus capensis (Diptera: Edited by A Pauw Bombyliidae), which landed on the anthers and then moved toward the perianth tube, inserting its proboscis and thorax into the upper perianth tube, evidently foraging for nectar. Pollen loads on the ventral body of flies were Keywords: passively transferred to receptive style branches of flowers visited later. This is the first record in Iridaceae of Iridaceae potentially pollinating visits by Megapalpus or any bee-fly. Geissorhiza © 2013 SAAB. Published by Elsevier B.V. All rights reserved. Megapalpus New species Pollination Southern Africa Taxonomy Winter rainfall zone 1. Introduction capensis (Bombyliidae) which we hypothesize is a legitimate pollinator of the species. This is the first example of pollination by Megapalpus or Geissorhiza Ker Gawl. is a genus of 101 species in the tribe Ixieae for that matter any bee-fly in Iridaceae although pollination by long- Dumort. of subfam. Crocoideae Burnett of the Iridaceae, and has proboscid Nemestrinidae and Tabanidae is known for other species of been recently revised (Goldblatt and Manning, 2009). Largely Geissorhiza sect. Engysiphon, all with longer-tubed flowers (Manning restricted to the Greater Cape flora region (Born et al., 2006), it is and Goldblatt, 1997; Goldblatt and Manning, 2000, 2009). one of the larger genera of Iridaceae, extending from northern Namaqualand in Northern Cape to Grahamstown in eastern Cape, with 2. Species description a marked centre of diversity in between Nieuwoudtville in Northern Cape and Bredasdorp in Western Cape (Goldblatt, 1985; Goldblatt and 2.1. G. melanthera Goldblatt & J.C. Manning, sp. nov. Manning, 2009). The new species, Geissorhiza melanthera Goldblatt & J.C. Manning, is a narrow endemic of the western end of the Piketberg TYPE—Western Cape, 3218 (Clanwilliam): Piketberg, south-trending Mtns in northwestern Western Cape. The concentric corm tunics and sandy slope northeast of Farm Kanariefontein [Barkatsfontein], (−DA), relatively long-tubed zygomorphic flowers with declinate stamens and 2 Oct. 2012, Goldblatt & Porter 13850A (NBG, holo.; MO, PRE, iso.). style place the species in sect. Engysiphon (G.J. Lewis) Goldblatt of Plants 140–185 mm high. Corm ± ovoid, 6–8 mm diam.; tunics subg. Weihea (Eckl. ex Baker) Goldblatt, one of two subgenera of the concentric, light brown, fragmenting vertically into elliptic segments, genus. When first collected in September 2012 the beige-yellow flowers not accumulating. Stem smooth, suberect, flexed outward above with remarkable black anthers (for which the species is named and sheaths of upper two leaves, suberect, simple or with 1 branch from unique for the genus) were actively visited by the bee-fly Megapalpus uppermost leaf axil, flexed at base of first flower. Leaves usually 3(2), lowermost basal, suberect, 140–180 × ±1.3 mm, blades ± square in outline, margins raised into wings extended at 90° to blade surface, ⁎ Corresponding author at: B.A. Krukoff Curator of African Botany, Missouri Botanical Garden, P. O. Box 299, St. Louis, Missouri 63166, USA. sparsely ciliolate on edges, sticky outside with sand adhering, main E-mail address: [email protected] (P. Goldblatt). vein hardly thickened, plane and paler green between margins and 0254-6299/$ – see front matter © 2013 SAAB. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sajb.2013.03.005 P. Goldblatt, J.C. Manning / South African Journal of Botany 87 (2013) 22–24 23 main vein, upper leaves smaller than basal. Spike ± horizontal, flexuose, secund with flowers borne on upper side, main spike 6–12-flowered, branch with fewer flowers; bracts suberect, green, (12–)16–22 mm long, inner slightly shorter to ±1/2 as long as inner, 2-keeled and forked apically. Flowers zygomorphic, unscented, pale beige-yellow, with red ring at base of tepals and in tube, reverse of tepals sometimes flushed red, anthers black; perianth tube ± cylindric, 10–14 mm long, constricted in lower 8–9 mm and widening distally; tepals narrowly obovoid-oblong, ±24–26 × 7–8 mm, spreading at right angles to tube when fully expanded, inner slightly wider than outer. Stamens unilateral, declinate, extended ± horizontally; filaments ±5 mm long, red; an- thers unequal, laterals 5–6 mm long, central 6.5–7.0 mm long, sagittate at base, ±black, remaining straight and rigid after dehiscence with white connective exposed; pollen dark purple. Ovary cylindric-oblong, 5–6 mm long; style declinate, extended below filaments, dividing opposite upper 1/3 of anthers, style branches initially parallel, weakly divergent when receptive, ±2.7 mm long. Capsules and seeds unknown. Flowering time: late September to mid October. (Fig. 1). 2.2. Distribution Discovered in October 2012, G. melanthera is a narrow endemic of Fig. 2. Distribution of Geissorhiza melanthera. western end of the Piketberg Mtns (Fig. 2) in northwestern Western Cape. It grows on gentle, south-trending slopes in deep sand below rocky slopes. Plants were found both in unburned areas among clumps of restiads and low shrubs as well as in places burnt last summer, where they were more common. With so small range we suggest a conserva- tion status of VU, Vulnerable. 2.3. Diagnosis and relationships In its general aspect and size G. melanthera recalls species of sect. Engysiphon of the genus, particularly the small-flowered Geissorhiza helmei Goldblatt & J.C. Manning, also a narrow endemic of the Piketberg (Goldblatt and Manning, 2009). G. melanthera is, however, a slightly larger plant with larger, beige-yellow flowers with a perianth tube 10–14 mm long and spreading tepals 24–26 mm long. The flowers are zygomorphic with declinate stamens and style typical of the section, but the anthers are black and slightly elliptic with the central anther slightly long than the laterals. G. helmei has the smallest flowers in the section, with a perianth tube 4–5 mm long, tepals only about 12 mm long, and its conventional linear anthers become twisted and deformed after pollen release, as do the other species of the section. G. melanthera has the smallest corms in sect. Engysiphon, only 6–8 mm in diameter. The anthers of G. melanthera are its most striking feature, unusual for the genus not only in their black colour, but also in retaining their elliptical shape after releasing their pollen, with a portion of the connective exposed and showing white between the thecae. Dark purple anthers and purple pollen are common in the section but in other species the anthers lose their shape, shrinking and becoming deformed after releasing pollen. The leaves of G. melanthera are H-shaped in cross section with the margins having wings as wide as the leaf axis and held at right angles to the blade. The midrib is raised. Only the primary vascular bundles have sclerenchymatous phloem caps. This leaf type is characteristic of Geissorhiza exscapa (Thunb.) Goldblatt, which has larger flowers, and also pink-flowered Geissorhiza bonaspei Goldblatt and white-flowered Geissorhiza tenella Goldblatt. We infer that G. melanthera is allied to these species, all of which have a somewhat to significantly longer perianth tube at least 20 mm long (40–80 mm in G. exscapa). The remaining species of sect. Engysiphon,includingG. helmei, have leaves with the main vein strongly thickened and laterally expanded, and the Fig. 1. Geissorhiza melanthera, Goldblatt & Porter 13850A.A,flowering plant; B, detail of anther before (below) and after (above) dehiscence; C, T/S leaf. Scale bar: A, 10 mm; marginal wings are narrower (Goldblatt, 1985), the leaf outline thus B, 2.5 mm; C, 300 μm. Artist: John Manning. oblong (I-shaped) rather than square (H-shaped). 24 P. Goldblatt, J.C. Manning / South African Journal of Botany 87 (2013) 22–24 3. Pollination biology The flowers of G. melanthera have the appearance of being adapted for long-proboscid fly pollination, specifically the Moegistorhynchus– Phololiche pollination system (Manning and Goldblatt, 1997; Goldblatt and Manning, 2000) but the tube length, 11–14 mm long, is shorter than the minimum length of ±29 mm recorded for this guild (Pauw et al., 2009). In addition the perianth tube is constricted in the lower 8–9 mm which results in the nectar rising to the upper 3–4mmofthe tube. We confirmed the presence of nectar in G. melanthera but did not have the opportunity to examine nectar characteristics. Observa- tions for 2 h on two days showed visits to the fully open flowers only by the bee-fly M. capensis (Bombyliidae). Tepals of flowers open ±10:30 on warm days and begin to close again at 15:00.