Introduction
Didymoplexis verrucosa J. Stewart & Hennessy and Hetaeria heterosepala (Rchb. f) Summerh., two orchid species hitherto only known from Africa, are newly reported from Madagascar. Didymoplexis verrucosa was discovered by Jean-Philippe Castillon near Bekopaka in the Tsingy de Bemaraha in western Madagascar. It is the second species of the palaeotropical genus Didymoplexis Griff. to be recorded from Madagascar. Hetaeria heterosepala was collected during an inventory of the upper part of Montagne d'Ambre in northern Madagascar (Trigui, 2010). It represents the first record for Madagascar of this paleotropical genus of ca. 30 species.
Didymoplexis verrucosa J. Stewart & Hennessy in Amer. Orchid Soc. Bull. 49: 841. 1980 (Fig. 1).
Typus: South Africa: KwaZulu-Natal Province, Mtunzini Distr.: Farm “Twinstreams”, 15.VIII.1978, Garland s.n. (holo-: NU [NU0015603-0]; iso-: E, K [000242 212], PRE [PRE0633590-0], S [G-G-6945]).
Herb, holomycotrophic, glabrous, leafless. Tuber elongate, moniliform, branching, up to 90 mm long, 20 mm in diam. Scape erect, 10–15 cm tall, bearing two sheathing cataphylls at the base, 8- to 12-flowered; bracts spreading, ovate to triangular-ovate, 1–2 mm long. Flowers non-resupinate, white, 10–13 mm across; pedicel and ovary 10–16 mm long; sepals and petals connate into a short tube at the base; dorsal sepal oblong, obtuse or rounded at the tip, 6–8 × 3–4 mm, connate for 1–2 mm with the petals; lateral sepal similar but connate for 1 mm or less to the dorsal sepal; petals oblong, obtuse or rounded, 5–6 × 2–4 mm; lip erect-spreading, free, shortly clawed, transversely triangular, 3-lobed at apex, 5–6 × 8–9 mm; callus of two lines of small warts from base to tip, with a fleshy yellow ligule on the claw; column straight, 4 mm long. Capsule narrowly ovoidelliptic, 20 mm long, 10 mm in diam., pedicel extending erect to 100–200 mm as the capsule develops.
Distribution and ecology. — South Africa (N KwaZulu-Natal) and western Madagascar. In coastal forest on sand in South Africa and in forest on tsingy (eroded limestone) in Madagascar; 0–100 m.
Observations. — Jean-Philippe Castillon recently sent a photograph to Kew of a distinctive white holomycotrophic orchid, from Bekopaka in the Tsingy de Bemaraha in western Madagascar (Fig. 1), in which the flower and lip morphology was clearly visible. It proved to be Didymoplexis verrucosa, an orchid originally described by Stewart & Hennessy (1980) from a plant collected in KwaZulu-Natal in South Africa from coastal forest on sand. Unfortunately, no material of it was preserved as the photographer was on a holiday trip.
Hetaeria heterosepala (Rchb. f.) Summerh. in Bull. Misc. Inform. Kew 5: 207. 1934.
= Cheirostylis heterosepala Rchb. f., Otia Bot. Hamburg: 110. 1881. = Zeuxine heterosepala (Rchb. f.) Geerinck in Bull. Jard. Bot. Natl. Belg. 50: 120. 1980.
Typus: CAMEROON: Cameroon Mountains, 3000 f. [915 m], XI.1862, Mann 2130 p. p. (holo-: K [K000106606]; iso-: W).
Herb, perennial up to 20 cm tall. Rhizome fleshy, creeping, 3–4 mm in diam., rooting at the nodes. Leaves ovate, acute, 2.2–4.5 × 1–1.8 cm; petiole and sheath 8–12 mm long. Inflorescence densely racemose, 2–6 cm long, up to 20-flowered; bracts lanceolate, acuminate, 5–7 mm long, almost as long as the ovary. Flowers usually non-resupinate, with green sepals and white petals and lip; dorsal sepal elliptic, obtuse, 4– 5 × 1.7–2.5 mm, adnate to the petals to form a hood over the column; lateral sepals obliquely ovate, similar to dorsal sepal; petals obliquely oblong-elliptic, 4–4.5 × 1.5 mm; lip bipartite, 3.5–5 × 3–3.5 mm; basal part saccate, bearing 2 recurved, hooked calli at the base within; the apical lobe transversely oblong, emarginate, apiculate; column 2.5 mm long, with two linear, acute to obtuse, porrect arms at apex.
Distribution and ecology. — West, Central and East Tropical Africa and Northern Madagascar. This species occurs on forest floor in deep shade in dense wet forest; around 990 m in Madagascar.
Specimens examined. — MADAGASCAR. Prov. Antsiranana, DIANA Region: Montagne d'Ambre, versants est, alt. 990 m, 10.V.2008, Trigui, Razanajatovo & Ramandimbimanana 390 (G, TEF, K, P, MO, WAG).
Observations. — A terrestrial orchid (Trigui & al. 390) collected on Montagne d'Ambre in northern Madagascar proved to be a new record of Hetaeria heterosepala, previously known only from Tropical Africa where it ranges from Liberia to Cameroon and across the Democratic Republic of the Congo to North-east Tanzania. It could only be confused with species of Cheirostylis or Zeuxine, both of which are also characterized by non-resupinate flowers and a column that lacks the long apical arms. These genera are also each represented by a single species in Madagascar.
An annotated list of orchid species shared between mainland Africa and Madagascar is provided (Table 1). With the two new records, the total number of shared species amounts to 40, representing about 4.6% of the Malagasy orchid flora (862 species according to Callmander & al., 2011). Looking at their distribution, 95% of them occur in East Africa; 50% occur in southern Africa and 45% are distributed as far as West Africa. Some species also occur in the Comoros, the Mascarenes or the Seychelles. The two new Malagasy species records presented in this note illustrate very different cases: Didymoplexis verrucosa has a very restricted range in hot dry parts of South Africa and western Madagascar, where it grows on quite different substrates, whereas Hetaeria heterosepala occurs in moist forest throughout a large part of West, Central and East Africa, and a single known locality in northern Madagascar.
Fig. 1.
Didymoplexis verrucosa J. Stewart & Hennessy. First observation in Madagascar.
[Photo : J.-P. Castillon]
Table 1.
Orchid species distributed in both mainland Africa and Madagascar (based on Hermans & al., 2007 ; Cribb & Hermans, 2009; and further contributions) ; WA, CA, EA and SA: West, Central, East and southern Africa, respectively.
Acknowledgements
Financial support for fieldwork allowing collection of Hetaeria heterosepala was provided by grants from Sud Experts Plantes (SEP 348) and Marc Birkigt Fund from the Geneva Academic Society. This fieldwork was conducted under collaboration between the Département d'Ecologie végétale of the Université d'Antananarivo (DBEV) and the Conservatoire et Jardin botaniques de la Ville de Genève (CJBG). We thank Prof. Charlotte Rajeriarison, Dr. Edmond Roger, Dr. Patrick Ranirison, Mialy Harindra Razanajatovo and Solotiana Deraharilanto Raman dimbimanana from the DBEV and Madagascar National Parks (MNP). Many thanks to Nicolas Fumeaux at CJBG for sharing his large biblio graphic knowledge. We would like to compliment J.-P. Castillon, Reunion Island University, for having found Didymoplexis verrucosa for the first time in Madagascar and to thank him for allowing us to reproduce his photograph.
