Homalium rakotovaoi Appleq., 2020

Applequist, Wendy L., 2020, A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar, Candollea 75 (2), pp. 245-268 : 262-264

9. Homalium rakotovaoi Appleq. , sp. nov.

( Fig. 8 ).

Holotypus: MADAGASCAR. Reg. SAVA [Prov. Antsiranana]: Andapa, Doany, Andranomilolo , env. 13 km à l’W d’Andranopositra , 14°19'44"S 49°16'57 "E, 841 m, 2.XI.2006, fr., Rakotovao et al. 3228 ( MO-6175072 !; iso-: G [ G00341925 ] image seen, MO-6175714 !, P [ P05529033 ]!, TAN).

Homalium rakotovaoi Appleq. differs from H. leucophloeum (Tul.) Baill. in its often larger, ovate leaves with crenate to crenulate, often revolute margins, racemes with (1–)3–7 flowers per node, and well-developed pedicels.

Tree to 25 m tall or shrub; twigs dark brown with conspicuous pale lenticels, glabrous. Leaves ovate (lanceolate to elliptical), (5.5–)6.7–15.7 × (2.8–) 3.5–6.5 cm, variably thickish to thin-textured; margin irregularly and shallowly crenate to crenulate (sometimes slightly undulate), often somewhat revolute; base rounded (often minutely attenuate at petiole junction) to convex, slightly oblique (very broadly cuneate); apex acuminate (acute, obtuse, or emarginate); both surfaces glabrous, drying brown to greenish, the upper surface usually brown, darker; secondary veins very little prominent; petiole sometimes (but not consistently) red, 9–16(–22) mm, glabrous. Inflorescences racemose, (3 –) 5 – 16 cm; peduncle 0.3 – 1.2(– 2.7) cm; rachis glabrous (sparsely pubescent); flowers (1 –)3– 7 per node; pedicels (1.5–)2.5 –6(– 8.5) mm, moderately pubescent. Flowers 4-merous, white; sepals oblong (slightly obovate), 1.4–2.2 mm, glabrous or glabrate, margins not ciliate; sepal glands broadly elliptical (orbicular), 0.4–0.6 × 0.3–0.4 mm; calyx cup sparsely pubescent; petals obovate, 2.7–6.2 mm, glabrous, margins not ciliate; filaments 0.8–1.5 mm; anthers broadly elliptical, 0.3 mm high.

Etymology. – Homalium rakotovaoi is named for Charles Rakotovao, collector of the type, to honor his many contributions to botany in Madagascar.

Vernacular names. – “Azoadala” (Reserves Naturelles 6017); “Hazoadala” (Randrianarivelo et al. 442, Saboureau s.n., Service Forestier 9280); “Hazoadala (p.[etites] f.[euilles])” (Reserves Naturelles 4182); “Janganita fotsy” (Reserves Naturelles 1751); “Malazovoavy” (Decary 1030).

Distribution, ecology and conservation status. – Homalium rakotovaoi is native to northern Madagascar ( Fig. 2 ). It has been reported to occur in mid-altitude humid forest (though much of the potential range is probably subhumid) and to occur near rivers or on slopes, once on limestone. The EOO is estimated as 3434 km ², and the AOO as 36 km ², with some collections’ localities estimated with a low degree of accuracy, but with fewer than ten distinct populations known. Several collections are from various portions of the protected area of Tsaratanana.

The conservation status is tentatively estimated as “Least Concern” [LC].

Notes. – Homalium rakotovaoi has usually ovate leaves with often conspicuously crenate to wavy (though sometimes subentire) margins, large clusters of long-pedicellate flowers, narrow acute sepals, and 4-merous flowers that are glabrous or glabrate except for sparse pubescence on the calyx cup, the sepals and petals without ciliate margins. The latter floral characters indicate a closer relationship to the H. leucophloeum group than to H. albiflorum s.s. Most of the species in that group have usually more or less elliptical leaves with often entire margins and flowers in groups of up to 3 or 4, with short pedicels or sessile. Two species, H. rakotovaoi and H. vohitsiandrianense Appleq. (see below), have usually ovate leaves, well-developed pedicels, and flowers sometimes in larger groups (in this species, at the extreme, up to 7). They are presumed to be sister species. Homalium vohitsiandrianense , which is known only from a southeastern massif, has smaller, sometimes broadly ovate leaves with usually acute apices, shorter racemes, and huge sepal glands.

Ranirison & Nusbaumer 914 has large (to over 15 cm long, 8 cm broad), glabrous leaves with often acuminate apices and flowers in clusters of several with well-developed pedicels. However, the leaves are elliptical and it has long-peduncled pubescent inflorescences and large pentamerous flowers with pilose calyces (with unusually long narrow sepals) and pubescent petals. It is plausibly interpreted as a hybrid of H. rakotovaoi and H. albiflorum . Although H. rakotovaoi has not been collected near Daraina, its presence in that region is predicted based on the existence of this intermediate. However, an alternative possibility is that this collection is a distinct, locally endemic species that happens by coincidence to have intermediate morphology. Further collections from Daraina would be desirable.

Paratypi. – MADAGASCAR. Reg. DIANA [Prov. Antsiranana]: Tsaratanana, Antsahabe riv , 14°00'45"S 48°46'40"E, 700–1200 m, 27.VII.2000, fl., Antilahimena et al. 506 ( BR, K, MO, P) ; Tsaratanana Massif , path from Mahatsabory Mica and Mangindrano, W of Befosa River , 14°12'22"S 48°57'14"E, 1400 m, 21.X.2001, fl. & fr., Birkinshaw et al. 993 ( G, MO, P) ; env. de Mt. Tsaratanana , 1700 m, XI.1912, fr., Perrier de la Bâthie 6703 ( P) ; ibid. loc., 1500 m, XI.1912, fr., Perrier de la Bâthie 6704 ( P) ; 10 km NE de Mangindrano, forêt d’Antsahivo , 14°14'34"S 49°00'31"E, 1249 m, 29.XI.2005, fr., Randrianarivelo et al. 442 ( MO, P, G) ; Marovato, Ambanja , 28.IX.1948 or 29.VIII.1948, fl., Réserves Naturelles 1751 ( P [2 sheets]) ; ibid. loco, 19.VII.1952, fl., Réserves Naturelles 4182 ( P [2 sheets]) ; Andavaka, Ambanja , s.d., fl., Saboureau s.n. ( P) ; Andavaka , 20.X.1949, fl., Service Forestier s.n. (Rakoto 6) ( MO). Reg. SAVA [Prov. Antsiranana]: Ampoanaomby [ Amponaomby ], Andapa , 3.XII.1953, fl. & fr., Service Forestier 9280 ( P, G). Reg. Sofia [Prov. Mahajanga]: Maromandia ( Bemaneviky ), 23.IX.1922, fl., Decary 1030 ( P) ; 7 km NE Mangindrano près de la rivière Antsahivo , 14°14'27"S 49°00'18"E, 1233 m, XI.2005, fr., Rakotovao & Jaovazaha 2628 ( MO, P) ; Tsaratanana, sommet, 1.VII.1953, fl., Réserves Naturelles 6017 ( P).

Probable hybrid specimen. – MADAGASCAR. Reg. SAVA [Prov. Antsiranana]: Daraina, forêt de Bobankora , 13°13'36"S 49°45'31"E, 320 m, 26.I.2005, fl., Ranirison & Nusbaumer 914 ( G, MO, P, TEF).

Figures

Fig. 8. – Homalium rakotovaoi Appleq. A. Flowering branch; B. Inflorescence; C. Flower. [Rakotovao et al. 3228, TAN] [Drawings: R.L. Andriamiarisoa]

Fig. 2. – Map of representative distributions of species in the Homalium albiflorum complex, approximated as necessary.