Gnidia razakamalalana Z.S.Rogers, 2006

Rogers, Zachary S., 2006, A new species of Malagasy Gnidia and the lectotypification of Octolepis decalepis (Thymelaeaceae), Adansonia (3) 28 (1), pp. 155-160 : 156-159

Gnidia razakamalalana Z.S.Rogers , sp. nov.

( Fig. 1 )

Haec species a Lasiosiphone ambondrombensi hypanthio c. 5 (vs. 1.4-1.6) cm longo, calycis lobulis 1.7-2.2 (vs. 0.6- 0.8) cm longis, inflorescentia uniflora (vs. 8-15 flora) atque foliis supra glabris (vs. dense pubescentibus) differt.

TYPUS. — Madagascar. Prov. Toliara, Fivondronona, Fort Dauphin , Firaisana Iaboko , Fokontany Antsotso , forêt de Ivohibe, 112 m, 24°34’35”S, 47°11’55”E, 29.XI.2005, fl ., R. Razakamalala , E. Ramisy & B. Mara 2670 (holo-, MO!; iso-, K!, P!, TEF!).

PARATYPE. — Madagascar. Prov. Toliara, Région de l’Anosy, District Fort Dauphin , Commune Iabakoho , Quartier Antsotso , forêt dense humide de basse altitude d’Ivohibe-Bemangidy , sur dôme rocheux, 90 m, 24°34’09”S, 47°12’23”E, 12. II .2006, fl., J. Rabenantoandro , P. P . Lowry II, E . Lowry , F . Randriatafika & M . Berger 1725 ( MO!, P!, TAN!) .

DESCRIPTION

Treelets 2 m tall; branches dichotomous, dark red, glabrous, covered with prominent leaf scars; internodes very short (c. 1 mm long near branch tips). Leaves exstipulate, spirally arranged, sessile or subsessile, persistent only at the tips of branches; petioles 0-0.3 mm long, densely sericeous; leaf blades elliptic or ovate-lanceolate, 4.5-8.4 cm long, 1-1.2 cm wide, length/width ratio 4-7:1, adaxially glabrous, abaxially densely sericeous, apex acute, margin entire, base obtuse-shortly decurrent or truncate; midrib impressed adaxially, raised abaxially; venation brochidodromous, inconspicuous or only faintly visible, more obvious abaxially. Inflorescences terminal, erect, 1-flowered, leaving prominent scars on older branches. Flowers tubular, diplostemonous, 5-merous, reddish-white, sessile or subsessile, surrounded by several involute leaves (each at least partly adpressed to the lower portion of the floral tube, the distal ones becoming smaller in size and lighter in color); hypanthium c. 5 cm long, subcylindrical, c. 1 mm in diam. near base, c. 3 mm in diam.at mouth, adaxially glabrous, abaxially covered by dense shorter sericeous-tomentose trichomes intermixed with some longer straight trichomes, indument more or less uniform along length of tube, articulation not seen; calyx lobes 5, spreading, lanceolate-elliptic, 1.7-2.2 cm long, 3.5-5 mm wide, more membranous than hypanthium, adaxially papilliate and sparsely tomentose-sericeous, trichomes shorter than those on the abaxial surface, abaxial indument similar to but not as dense as that on the tube, apex acute or apiculate, with a dense tuft of straight trichomes; petals 5, scale-like, alternisepalous, oblong, ovate, or subtriangular, 1.8-2.2 mm long, 0.7-1 mm wide, membranous, apex irregularly erose, 1-5-lobed, lobes of varying length; stamens 10; filaments fused for most of their length to tube, upper whorl of anthers positioned just below mouth, lower whorl 2-4 mm below upper whorl; anthers bithecal, basifixed, longitudinally dehiscent, introrse, oblong, c. 3 mm long, c. 0.5 mm wide, subsessile; subgynoecial disk cup-shaped, up to 0.7 mm tall, glabrous, membranous, apex irregularly lobed, sinuses mostly shallow; gynoecium pseudomonomerous; ovary ellipsoid, c. 2.2 mm long, c. 1 mm wide, apex covered with a tuft of straight trichomes, each 1.5-2.3 mm long, lower 1/2 to 2/3 glabrous, base tapering; ovules 1, apical; style lateral, 1.5-1.8 cm long, filiform, flattened, c. 0.3 mm wide, glabrous; stigma inserted, reaching c. 1.5 mm below lower whorl of anthers (i.e. located near middle of tube), fusiform, c. 4 mm long, c. 0.5 mm wide, densely papilliate. Fruits not seen.

DISTRIBUTION AND HABITAT

Gnidia razakamalalana appears to be a narrow endemic, with only one known population occurring

in subcoastal forest in SE Madagascar, at c. 100 m elevation. The species grows on a slope among exposed granite boulders on black sandy soil.

PHENOLOGY

This species flowers from November to February.

CONSERVATION STATUS

Gnidia razakamalalana is known from a single unprotected population. Given the apparent restricted range of the species, the area of occupancy is estimated to be no more than 10 km 2. Based on IUCN (2001) Red List criteria, the species is assigned a preliminary conservation status of Endangered (EN B1ab+B2ab).

DISCUSSION

Among Malagasy Thymelaeaceae , Gnidia razakamalalana most closely resembles Lasiosiphon ambondrombensis but can be easily distinguished by its much larger hypanthium (c. 5 vs. 1.4-1.6 cm long) with longer calyx lobes (1.7-2.2 vs. 0.6-0.8 cm long), 1-flowered (vs. 8-15 flowered) inflorescences, and larger (4.5-8.4 vs. 1.5-2.3 cm long) leaves with a glabrous (vs.densely pubescent) adaxial surface. See the note by Aymonin (1975) regarding the affinities between L. ambondrombensis and the mainland African species of Gnidia .

The hypanthium of Gnidia razakamalalana is quite unusual in the genus because of its large size (5 cm long) and apparent lack of articulation. Most species of Gnidia have hypanthia measuring 1-2 cm long with those of only a few species (e.g., G. anthylloides (L.f.) Gilg) capable of reaching c. 3 cm in length. In fact, G. razakamalalana may prove to have the longest hypanthium in the family. The floral tube of nearly all species of the genus is articulated (lacking in G. glauca (Fresen.) Gilg from Africa and G. gilbertae Drake from Madagascar), which is used as a distinguishing character of Gnidia . This articulation appears as a straight line located some distance above the ovary and develops into a plane of abscission as the fruit matures. When an articulation is present, the portion of the hypanthium above it falls away, while the part below persists and surrounds the developing fruit, the two forming a single dispersal unit. The flowers on the type material of G. razakamalalana do not show any trace of an articulation but the abscission line in some species (e.g., L. ambondrombensis ) will often not clearly develop until the fruit is nearly mature. Fruiting collections of G. razakamalalana will be needed to determine if the species truly lacks an articulated hypanthium.

ETYMOLOGY

It is with great pleasure that I name Gnidia razakamalalana in honor of Malagasy botanist Richard Razakamalala, who was the first person to collect this species and who has accompanied me with enormous enthusiasm on numerous field trips in search of Malagasy Thymelaeaceae .

Figures

FIG. 1. — Gnidia razakamalalana: A, habit; B, leaf; C, flower in longitudinal section; D, gynoecium and subgynoecial disk; E, stigma; F, petals. Razakamalala et al. 2670 (holotype). Scale bars: A-C, 1 cm; D-F, 1 mm.