Aerangis bovicornu Hermans, 2021

Hermans, Johan, Rajaovelona, Landy & Cribb, Phillip, 2021, New species in Orchidaceae from Madagascar, Kew Bulletin 76, pp. 39-56 : 40-41

Aerangis bovicornu Hermans sp. nov.

Type: Madagascar, Fianarantsoa prov., near Ankazomivady, in lee side of large inselberg, 1797 m, Dec. 1997, Hermans 8179 (holotype K!) .

http://www.ipni.org/urn:lsid:ipni.org:names:77214543-1

Short monopodial epiphytic herb up to 5 × 6.5 cm, with a short woody stem c. 8 mm in diam., covered in brown corrugate sheaths, bearing numerous somewhat hirsute orange-brown roots becoming grey with age, c. 1.5 mm in diam. Leaves 3 – 5, leathery, on a short 3 – 5 mm conduplicate petiole, ovate to elliptic, 20 – 33 × 16 – 22 mm, somewhat convex, emarginate at the tip, laevigate, more or less brownish-orange on the upper surface, greyish-green, punctate underneath with the central vein darker. Inflorescence very short, up to 2.5 cm long, bearing 2 – 3 flowers and an aborted bud. Rachis 3 – 5 mm in diam., orange-brown, almost entirely covered with 2 – 3 conduplicate to almost tubular bracts, 3.4 – 4.8 × 1.8 – 2.1 mm. Floral bracts thin, amplexicaul, 1.8 – 2.3 × 1.8 × 2 mm. Flowers c. 10 × 10 mm without the spur, about 10 mm apart, stellate, not opening fully; petals, sepals and lip white with the tips sometimes tinged with orange, the ovary and spur orange-brown, the buds green. Pedicel and ovary straight, rounded, slightly ridged, 8 – 12 × 1.9 – 2.3 mm. Dorsal sepal ovate-elliptic, acuminate, 7.8 – 8.6 × 3.6 – 3.9 mm, narrowed, reflexed towards the base. Lateral sepals obliquely lanceolate, acuminate, 8.7 – 8.9 × 3.5 – 3.7 mm. Petals ovate elliptic, obtuse, 8.3 – 8.6 × 3.8 – 4.1 mm. Lip ovate-lanceolate, attenuate, 7.6 – 8.2 × 3.9 – 4.1 mm; spur slender, horn-shaped, terete at the tip, a little broadened towards the base, 20 – 23 × 0.9 – 1.3 mm. Column short, stout, slightly winged, broadly mucronate at the apex, rostellum ligulate-ensiform, up to 5 mm long; anther broadly obovoid with a small rounded swelling at the apex, up to 1.4 × 1.6 mm; pollinia globose c. 0.8 × 0.6 mm, stipes short and slender, viscidium elongate, narrow. Seed capsule fusiform, glabrous, brown, 16 × 5 mm. Figs 1A, B ; 2 .

RECOGNITION. Aerangis bovicornu is a few-flowered compact plant with small flowers that do not open fully, ovate to elliptic leaves which are brownishorange on top and greyish-green underneath; the stellate flowers have a short horn-shaped spur and white perianth with an orange-brown ovary and spur and long rostellum and anther with a small rounded swelling at the apex. It is undoubtedly most closely related to Aerangis fastuosa (Rchb.f.) Schltr. ( Schlechter 1914: 598) ( Fig. 1C ) but differs substantially in its flowers which are consistently a third of the size, the straight slender, up to 23 mm long, spur which is consistently much shorter (vs a minimum of 76 mm in A. fastuosa ), the perianth tips and spur coloured brownish-orange (vs generally white), the narrower column apex and the obovoid anther with a small rounded swelling at the apex (vs conical with a long beak). The new species flowers from December to January whilst Aerangis fastuosa flowers earlier from June to November. Table 1 shows a comparison of characteristics and measurements based on 28 herbarium specimens [Lawrence (BM00540114); Baron s.n. (K); Hillerman 12, 13, s.n. (K); Kotozafy 334 (K); Pettersson & Nilsson 380 (K); Hermans 3240, 3766, 4139, 4277, 5169, 5449, 5485, 6664, 6666 (all K); Humblot s.n. (W-R46259); Hort. (W-R30844); Hildebrandt 4207 (W); cult. Lendy (W-R29591); cult. Low (W-R28278); G. Fischer et al. FS1586-2004 (WU); Humbert & Cours 17779 (P); Bosser 14643, 16423 (P); Decary 18402 (P); Rakotoson 12418RN (P); Bernardi 11128 (P)].

DISTRIBUTION. Endemic to south-central Madagascar, Fianarantsoa province, only known from the type collection.

HABITAT. Epiphyte on small moss- and lichen-covered trees in remnants of forest on granite inselberg. Elevation c. 1800 m.

CONSERVATION STATUS. Recent observations by one of the authors (JH) found only six plants remaining in the type locality, one bearing an immature seed capsule. The area has now been cleared for cultivation of Pelargonium , grown increasingly in the region for the production of essential oils. Aerangis bovicornu has an EOO less than 100 km 2 and an AOO less than 10 km 2 and only one threat location is identified. In addition, the number of mature individuals is estimated to be less than 50. The species is therefore assessed as Critically Endangered CR with Criterion D.

FLOWERING TIME. December to January.

ETYMOLOGY. The epithet refers to the typical shape of the spur, resembling a bull’ s horn, especially that of the local Madagascan zebu cattle.

NOTES. The genus Aerangis Rchb.f. ( Reichenbach 1865: 190) now comprises 59 species; they are largely epiphytes confined to Africa and the Madagascar region, apart from one species which occurs both in eastern Africa and Sri Lanka. There are 28 species in Madagascar, Réunion and the Comoros with 20 of them endemic to Madagascar.

Aerangis fastuosa ( Fig. 1C ) was first described by H. G. Reichenbach as Angraecum fastuosum Rchb.f. ( Reichenbach: 1881c: 748) based on a plant collected by Léon Humblot in Madagascar and imported into England by the nurseryman Frederick Sander. The type specimen consists of two flowers and a drawing in the Reichenbach herbarium in W (number 46259). Reichenbach described it as having rugose leaves on the upper surface, a narrow lip and a long caudicula immersed in the spur. Two weeks later ( Reichenbach 1881d: 844) added notes on a specimen from the same source and grown by Sir Trevor Lawrence, as equal to his type in all details, but having an obovate rounded lip, instead of a narrow acute one, and suggested either that M. Humblot’ s plant was a peloric form, or that there were two closely allied species. Joseph Hooker (1891: t.7202) later commented on Reichenbach’ s confusing descriptions. He added that the rugosity of the leaf occurs only after flowering and is hardly perceptible. He referred to the 1885 illustration of a Lawrence plant in Gardener’ s Chronicle ( Masters 1885: 533) as a good likeness. Subsequently a great number of plants found their way into European collections and the variability of the species became evident as recognised by Perrier de la Bâthie in 1941 (pp. 93 – 95) when he described six varieties of the species, none being validly published because they lacked Latin descriptions. He also mentioned that they may well be separate species, all coming from different localities, a long way from each other. All are only represented by very few herbarium specimens and it is difficult to define constant characteristics. Five of the varieties, notably var. francoisii , var. grandidieriana , var. maculata , var. rotundifolia and var. vondrozensis (Perrier 1941: 93 – 95) are generally accepted as local forms of one variable species ( Stewart 1986a: 905; Hermans et al. 2007: 12; La Croix 2014: 149), the stated variation was mainly in the leaf shape and texture. The sixth, var. maculata (Perrier 1941: 95) was considered by Bosser (2006: 50) to be Aerangis punctata J.Stewart (1986b: 1120) . A seventh, Aerangis fastuosa var. angustifolia H.Perrier (1941 : 95), was considered an immature form of Aerangis modesta (Hook.f.) Schltr. , ( Schlechter 1914: 600). At first sight Aerangis bovicornu could be considered another local variant of Aerangis fastuosa , especially as it comes from a relatively accessible region but closer examination proves otherwise. They share the leaf shape, short rachis, shape of the perianth and the long rostellum but size of all the floral parts, spur length, column and anther shape and colour are all very different. Table 2 outlines the main characteristics of the different variants, none corresponding with Aerangis bovicornu . The characteristics of the new species were found to be consistent within the local colony of about 20 plants which consisted of plants with flowers that were just opening and others that had almost wilted.

Figures

Fig. 1. A, B Aerangis bovicornu. A plant in habitat; B plant and flowers; C Aerangis fastuosa for comparison. PHOTOS: JOHAN HERMANS.

Fig. 2. Aerangis bovicornu. A habit; B flower; C dorsal sepal; D lateral sepal; E petal; F lip; G column and lip side view; H column, front view; J column, front view, anther cap removed; K anther cap, dorsal view; L anther cap, ventral view. From spirit material Hermans 8179. DRAWN BY JUDI STONE.