AFRICAN

ORCHIDS

Microcoelia caespitosa (Rolfe) Summerh. in J.Hutchinson & J.M.Dalziel, Fl. W. Trop. Afr. 2: 454 (1936).
Homotypic Synonyms:
Angraecum caespitosum Rolfe in D.Oliver & auct. suc. (eds.), Fl. Trop. Afr. 7: 150 (1897).
Gussonea caespitosa (Rolfe) Schltr., Beih. Bot. Centralbl. 36(2): 91 (1918).
Heterotypic Synonyms:
Angraecum crinale De Wild., Not. Pl. Util. Congo 1: 320 (1904).
Angraecum micropetalum Schltr., Bot. Jahrb. Syst. 38: 23 (1905).
Angraecum andersonii Rolfe, Bull. Misc. Inform. Kew 1912: 134 (1912).
Gussonea micropetala (Schltr.) Schltr., Orchideen: 592 (1914).
Angraecum bieleri De Wild., Bull. Jard. Bot. État Bruxelles 5: 182 (1916).
Gussonea bieleri (De Wild.) Schltr., Beih. Bot. Centralbl. 36(2): 91 (1918).
Gussonea crinalis (De Wild.) Schltr., Beih. Bot. Centralbl. 36(2): 91 (1918).
Microcoelia bieleri (De Wild.) Summerh., Bot. Mus. Leafl. 11: 151 (1943).
Microcoelia micropetala (Schltr.) Summerh., Bot. Mus. Leafl. 11: 155 (1943).
Description:
Stem short, in older specimens often ± stout and noticeably swollen at the joints with the inflorescences, rarely proliferous, (2-) 10—31 (—45) x (2—)2.5—5(—7) mm. Scale-leaves acuminate, with 6-7 (-8) nerves, up to 5 (-7) mm long. Roots few to many, long, mostly loosely attached to the substrate, ± pendulous, ± undulating and twisting, much branched distally, terete, smooth, up to 90 cmx(1.0-) 1.5-2.5 mm. Injlorescence(s) ± erect-spreading, up to 30 (-65) mm long, up to 10 (-18) simultaneously, usually dense, each with up to 22 flowers; peduncle short, up to 10 mm long; rachis ± straight to indistinctly flexuose, ± terete; bracts sheating, acute to subacute, with 3-5 nerves or occasionally slightly more, towards the apex of rachis gradually decreasing to 1-nerved, up to 2.0 (-3.0) mm long. Pedicel long, ± terete, indistinctly curved, (4.2-) 4.7-8.2 (-9.4) mm long; ovary ± straight, indistinctly furrowed, 1.1-2.9 x 0.3-0.7 mm, greenish white. Flowers ± horizontal, up to 17.5 mm long including ovary and pedicel; whitish or fading into greenish white, sepals with a central dark greenish line, labellum with a ± triangular central dark green blotch, spur apex tinged in light green or not, anther and column green. Glandular hairs very sparse or absent on rachis, base of bracts, pedicel, ovary and at the base of the tepals. Dorsal sepal hooded, ± oblong, obtuse to subacute, 3-nerved, with a ± thickened central nerve, (2.2-) 2.5-3.5 (—4.2) x 1.0—1.9(—2.2) mm. Lateral sepals asymmetric, ovate, obtuse to subapiculate, ± convex, with 3 nerves, central nerve slightly thickened, 2.7—4.1(—5.2) x ( 1.6—)2.0—2.6 (-2.9) mm. Petals obovate, obtuse or subacute, with one occasionally branched nerve, (2.1-) 2.3—3.1(—3.4) x (1.0—) 1.2—1.8(—2.4) mm. Labellum small, 3-lobed; mid-lobe ± triangular-shaped , flat or ± cupshaped, straight or deflexed, 3 main nerves with lateral branches; side-lobes indistinct, ± thickened, with a well developed thickening on each side of spur mouth, (1.7—)2.5—3.6(—3.9) x (1.0—) 1.1—1.9(—2.1) mm; mid-lobe alone up to 2.3 mm long; spur long, ± vertically pendant, basal part distinctly constricted, central part ± inflated, tapering into an indistinctly inflated obtuse apex, (6.5-)7.4-1.3(—14.2) mm long, the widest part up to 2.3 mm in diameter. Column elongated, straight to slightly erect 1.2-2.2 (-2.7) mm long, 0.6-1.1 mm high; androclinium shallowly excavated, with a distinct central thickening; rostellum lobes long, inserted from ± the middle of the column, bifid from ± the base, subacute, ± porrect.when mature, in a premature stage pointing into the spur mouth, (1.0—) 1.2—1.7(—2.0) mm long. Anther hemispherical, at the base bivalved, tapering into a distinctly curved, obtuse beak-shaped apex, (0.8—) 1.0—1.6 (—1.7) x (0.5—)0.9— 1.3(—1.4) mm. Pollinia ± globose; in side view ± orbicular to broadly elliptic, (390-)460-620(-660) x (390—)430—570(-610)// m; in median section indistinctly asymmetric, orbicular or elliptical to obovate, up to 560 pm thick, whitish cream. Stipes in side view distinctly sigmoid, spathulate, shallowly channelled, apically obtusely triangular. 1.1—1.5(—1.8) x 0.2-0.4 mm in natural position, greenish; viscidium long, convex ± flattened dorsally, oblong to obovate, apically rounded to subacute and distinctly connate with stipes, basally ± truncate, (1.1—) 1.3—1.7(—1.8) x 0.4—0.5(—0.6) mm, membranous. Capsule ± fusiform to broadly elliptic, 8-11 x 3-5 mm; pedicel long, often distinctly curved, up to 5.0-9.4 mm long. Seeds fusiform to ± bottle-shaped, testa cells narrowly elongate (in a dry state), with club-shaped to ± loop-shaped and more sparsely with more hookshaped processes; anticlinal walls ± sulcate with finer striations and sometimes indistinctly spirally sculptured, terminally mostly extended into ± spreading processes, 350-640 x 30-60 µm. Scent faint, ± sweet; on the whole only fragmentarily recorded, which could be an indication of a nocturnal periodicity.
Habitat:
Rain forest, often in the vicinity of rivers. Occasionally found in plantations and secondary forests. Epiphytic, mostly on branches of the understorey vegetation. Altitude, c. 50-1100 m.
Flowering period:
Mainly located to the transitions to the main rains.
Cultivation:
As given for the genus, hot to warm growing epiphyte.
Notes:
Microcoelia caespitosa may be recognised by the short inflorescences, long spur wider at both apex and base and the remarkable rostellum. This is deflexed at first and adpressed (perhaps adnate) to the column but the distal half projects forwards and upwards for an equal distance so as to be level with the anther. This upright part bears the long oblanceolate viscidium, the stipes being V-shaped to fit the rostellum and slightly widened above where the globose pollinia are attached.
Distribution:
W. Trop. Africa to Uganda
References:
A Monograph of the Genus Microcoelia [Orchidaceae] Jonsson 1981; Flora of Tropical East Africa Orchidaceae Part 3 Cribb 1989; Angreacoid Orchids Stewart, Hermans and Campbell 2006; WCSP (2017). 'World Checklist of Selected Plant Families. 03.03-2017; http://apps.kew.org/wcsp/
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