Angraecum gereauanum Stévart & Jecmenica, Phytotaxa 323: 147 (2017).
Homotypic Names:
Conchograecum gereauanum (Stévart & Jecmenica) Szlach. & Grochocka, Richardiana, N.S. 2: 92 (2018).
Description:
Herbaceous, monopodial, epiphyte herbs. Stem up to 9 cm long, intemode about 1.5 cm; cross section terete, whereas younger parts appear winged. Leaves alternate, edges apart or touching, elliptic-oblong in shape, 8.0-13.0 x 1.5-2.5 cm, apex obliquely bilobed with a straight rounded larger lobe reaching 4 mm, whereas the shorter lobe ends dully, margins entire; up to 9 nerves on the blade. Inflorescence of indeterminate type, thick, erect, bearing 3 (or more) flowers that bloom in consecutive seasons on a single inflorescence; peduncle axillary, 3.0-3.5 cm, rather at the base of the stem. Bracts with a thick middle nerve narrowly enveloping the peduncle, not covering the base of the pedicel, ovate, 3 mm long. Flowers resupinate, white, tepals with greenish nerves slightly curved and pointed forward, opening diameter about 1.5 cm. Ovary and pedicel greenish, curved, 16-19 mm long. Dorsal and lateral sepals alike, 15-20 x 4-5 mm, elliptic, acute, thick with entire margins. Petals similar to sepals, 14.0-18.0 x 4 0-4.5 mm, elliptic, acute. Lip, pure white, 13.5-17.0 x 8.0-10.0 mm, orbicular, widest in the middle; margins slightly unequally crisply undulate two-thirds from the apex, apex acuminate, convoluted downwards and appearing bent when flattened, callus present in the form of a keel; spur 18-19 mm long, convolute with an elliptically swollen apex, greenish. Column with a bulging bifid rostellum, 3.5 x 2.5 mm. Anther cap 2 x 2 mm, round with a indented shallow cut at the tip; pollinia two, 1 mm, obovoid, each attached to a single elliptic stipe connected to an individual viscidium, tapering sharply on one and with sticky tissue on other side; two viscidia appear linked with a thin layer of tissue. Capsule not seen.
Etymology:
The specific epithet honours our colleague Roy E. Gereau of the Missouri Botanical Garden for his major contribution to the knowledge and the conservation of the African flora and for his editorial work correcting nomenclature rules and Latin translation of taxonomic manuscripts. The epithet gereauanum (an adjectival epithet) is used to commemorate a person and is preferred to a genitive form (gereaui) that should be used for the collector of a cited specimen (according to an old convention, Roy E. Gereau, personal communication, April 14, 2017).
Habitat:
This species is only known from one locality in dense forest of Bouvala Mountain Range in the Massif du Chaillu. The locality is characterised by a humid, marshy forest on a plateau at the bottom of the deep valley. The plant was found growing as an epiphyte on a vertical liana at a height of two meters above the ground, in a well-lit clearing. Other orchid species found nearby were Diaphananthe pellucida (Lindley 1844: 2) Schlechter (1914: 593) and Polystachya rhodoptera Reichenbach (1858: 214).
Flowering phenology:
Flowering in the field found in October, whereas in cultivation flowering occurred in August-September.
Notes:
Angraecum gereauanum Stevart & Jecmenica is similar to A. affine Schlechter (1905: 19) but differs from it in the shorter and slightly winged stem (3-9 vs. 10-20 cm), the larger resupinate flowers (sepals 15.0-17.0 vs. 9.0-11.5 mm), the orbicular lip (vs. ovate-elliptic) with constricted acuminate apex (vs. acute, no constriction) and the undulate lip margins. This species is closely related to Angraecum geerinckianum considering the appearance of the flower, but it has smaller floral parts, e.g. dorsal sepals (15-20 vs 21-23 mm), petals (14.0-18.0 vs. 19.0-20.5 mm) and lip length (13.5-17.0 vs. 18.0-19.0 mm). It differs significantly from the latter in leaf shape (elliptic-oblong vs. broadly elliptic) and flower colour (white vs. whitish pinkish-orange).
Distribution:
Gabon
References:
Taxonomy of Atlantic Central African orchids, 6: three new species of Angraecum sect. Afrangraecum (Orchidaceae, Angraecinae) from Gabon and Sao Tomé Phytotaxa 323 (2): 143–158,2017 by Vincent Droissart and Tariq Stévart
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