Homalium pseudoracemosum Appleq., 2020

Applequist, Wendy L., 2020, A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar, Candollea 75 (2), pp. 245-268 : 260-262

8. Homalium pseudoracemosum Appleq. , sp. nov. ( Fig. 7 ).

Holotypus: MADAGASCAR. Reg. Sofia [Prov. Mahajanga]: forêt de Betsitindry , Ambato, distr. Befandriana, 24.X.1956, fr., Service Forestier 16408 ( MO-2818801 !; iso-: P [ P04679193 ]!).

Homalium pseudoracemosum Appleq. differs from H. albiflorum (Boivin ex Tul.) O. Hoffm. in having usually mostly lanceolate to ovate leaves, consistently short-branched racemiform panicles with glabrous or glabrate rachises, and flowers smaller, usually 4-merous, with petals glabrous except margins sometimes sparsely ciliate.

Tree to 20 m tall, 38 cm dbh; twigs dark brown later becoming pale brown, glabrous. Leaves lanceolate to ovate, narrowly elliptical, or elliptical, (4.8–)6–13.5(–14) × 2.4–5.5(–5.8) cm, thin-textured; margin irregularly crenulate (to crenateserrulate) or subentire; base convex (often short-attenuate at extreme base); apex short-acuminate (to acute, rounded, or obtuse); both surfaces glabrous, drying brown, often darker (to blackish) adaxially (rarely greenish adaxially); secondary veins slightly prominent; petiole (7–)9–14(–17) mm, glabrous. Inflorescences short-branched paniculate, (3.5–) 6– 13.5 cm; peduncle 0.7–3.5 cm; rachis glabrous or glabrate (branches sometimes sparsely minutely pubescent); flowers mostly in clusters of 2– 4(–5), many or most clusters borne on small inconspicuous branches; pedicels 0.5–3 mm, short-pubescent. Flowers 4(5)-merous, greenish to yellow; sepals oblong to broadly ovate (suborbicular), (1.3–) 1.5 – 2.5 mm, sparsely pubescent outside or glabrous, margins ciliate; sepal glands broadly elliptical, 0.6–0.8(–1) × 0.5–0.7 mm; calyx cup sparsely short-pubescent; petals obovate, 3–5.5 mm, little accrescent, glabrous except margins sometimes sparsely short-ciliate; filaments 1–1.5 mm; anthers broadly elliptical (to transversely elliptical?), 0.2–0.3 mm high.

Etymology. – Homalium pseudoracemosum is so named because its inflorescences appear on casual observation to be racemose, but are actually paniculate.

Vernacular names and uses. – “Ampimba” (Reserves Naturelles 2137); “Apimba” [?] (Service Forestier 3994); “Ampiniba” (Reserves Naturelles 4229); “Hazoamboa” (Louvel 168); “Hazomby” (Service Forestier 3917); “Lalipito” (Service Forestier 4445); “Mampisaraka” (Service Forestier 7796); “Revy” (Service Forestier 10517); “Saripapy” (Service Forestier 10875); “Taindalitra” (Service Forestier 15143); “Trongindambo” (Service Forestier 12026, 26203 [Sakalava dialect]).

Wood is used for construction and manufacture of planks (Service Forestier 16408, 26203).

Distribution, ecology and conservation status. – Homalium pseudoracemosum has been widespread in the dry western regions of Madagascar, with a latitudinal range extending from Menabe to Sofia and possibly DIANA ( Fig. 2 ). The two specimens from the DIANA region in the extreme north are atypical and are tentatively placed here. The species is reported to occur on limestone.

Homalium pseudoracemosum has probably occurred in more than ten populations, though locality data are poor in many cases, and in protected areas including the Bemaraha reserve, Namoroka, and (an atypical specimen) Montagne d’Ambre. Therefore, by standard application of the IUCN criteria, its conservation status would be assessed as “Least Concern”. However, the fact that only one atypical recent collection exists is of great concern. The case of this species may be compared to that of H. albiflorum , which has a similarly broad western-to-northern distribution, but has been collected from four regions since 1990. From historical data, the EOO of H. pseudoracemosum would be estimated as 140,994 km ² (including the DIANA populations) and the AOO as 72 km ². The vast majority of the potential habitat is unprotected and has been destroyed or severely degraded by human activity since the 1940s and 1950s, when most collections were made. As in the case of H. phillipsonii , it is probable that several of the historically collected populations no longer exist. Therefore, it is suggested that the conservation status of this species should be estimated as, minimally, “Vulnerable” [VU B2ab(iii)] because of the small AOO, presumably fewer than 10 surviving populations, and severe, continuing decline in area and quality of habitat.

Notes. – Homalium pseudoracemosum is distinguished by its short-branched racemiform panicles and lanceolate to ovate or elliptical leaves. Elliptical leaves (as on the atypical Andrianantoanina & Bezara 857) are often at the lower end of the size range, suggesting that they could be immature. The maximum size of the flowers appears to be smaller than in most species of this section, with the petals less strongly accrescent than most. This species occurs in much of the same range as H. albiflorum , which has usually elliptical leaves, usually racemose (though occasionally narrowly paniculate) inflorescences, pubescent rachises and flowers, and usually 5, somewhat larger petals. Homalium albiflorum is the only other species that ever has panicles of this form. The two are suspected to be closely related and to hybridize. However, H. pseudoracemosum also shows possible affinities to the H. leucophloeum group of mostly eastern species in its usually 4-merous, nearly glabrous sepals, petals, and inflorescences. Thus H. pseudoracemosum appears in some ways to represent an intermediate between these species groups.

Species of the H. albiflorum complex are generally described as having white or whitish flowers, when the color is reported, although H. leucophloeum is said to have pale greenish to pale yellowish flowers. Andrianantoanina & Bezara 857, one of the atypical extreme-northern specimens of H. pseudoracemosum , has label data reporting that the calyx is green and the corolla yellow. It is unclear whether this unusual report is due to life stage or differing interpretations of lightly pigmented petals, or whether this species indeed has a significantly different and darker flower color than most of its relatives. If the latter, it would provide another distinguishing feature in the field.

Several specimens appear morphologically intermediate between H. pseudoracemosum and H. albiflorum . Those from Ankarana have quite narrow leaves, inconsistently branched inflorescences with pubescent rachises, and pubescent flowers. Other narrow-leaved specimens possibly representing introgression between the two species are treated above under H. albiflorum . Leandri 356 was probably collected around the same time as Leandri 357, which is identified as H. albiflorum . This specimen has some features that are more consistent with H. pseudoracemosum , including sometimes narrow leaves, usually (but not always) glabrous rachises, and petals glabrous except for cilia. The bracts are cup-shaped and unusually large for either species (a feature also sometimes seen in the Ankarana specimens). No other possible parental species are known from near Bemaraha.

Paratypi. – MADAGASCAR. Reg. Boeny [Prov. Mahajanga]: Plateau d’Ankara , VIII.1900, fr., Perrier de la Bâthie 1090 ( P) ; Andrengy [ Namoroka ], Soalala , 21.I.1950, fl. & fr., Réserves Naturelles 2137 ( G, P [2 sheets]) ; R.N. 8 [ Namoroka ], Andranomavo, Soalala , 5.VIII.1952, fr., Réserves Naturelles 4229 ( P [2 sheets]) ; Belalanda, Soalala , 9.VIII.1951, fl., Service Forestier 3994 ( P). Reg. DIANA [Prov. Antsiranana]: Montagne d’Ambre, 8 km E de Bobakilandy ( Antsanavo ), 12°37'37"S 49°06'40"E, 533 m, 11.VII.1995, fl., Andrianantoanina & Bezara 857 ( BR, G, K, MO, P) ; Nosy Mitsio, X.1952, fr., Perrier de la Bâthie 18767 ( P). Reg. Melaky [Prov. Mahajanga]: E du Bemaraha , VIII.1943, fr., Herb. Jard. Bot. [Cours] 6192 ( P [2 sheets]) ; Antsingy, Antsalova , 29.X.1954, fr., Service Forestier 12096 ( P) ; Antanimbaribe, Morafenobe , 6.VIII.1955, fr., Service Forestier 15143 ( P) ; Forêt de Beandrao, Ankazomandiladongo, canton and distr. Antsalova , 23.IX.1966, fr., Service Forestier 26203 ( P). Reg. Menabe [Prov. Toliara]: Bassin de la Tsiribihina au N de Morondava , s.d., fl., Louvel 168 ( P) ; Dabora, Morondava , 18.VIII.1951, fr., Service Forestier 3917 ( P) ; Marofototra, Marovoay, Morondava , 15.XII.1951, fr., Service Forestier 4445 ( P) ; Ankilimidahy, Belo / Tsiribihina , 1.VII.1953, fr., Service Forestier 7796 ( P) ; Torrent à une trentaine de km à l’W du Betafo, sur la route de Miandrivazo, 26.VIII.1953, fl., Service Forestier 8429 ( P) ; Ankilizato, distr. de Mahabo, 26.VI.1954, fl., Service Forestier 10517 ( P) ; forêt d’Antabefotsy , Ankazomanga, Miandrivazo , 14.IX.1954, fr., Service Forestier 10875 ( P).

Possible hybrid specimens. – MADAGASCAR. Reg. DIANA [Prov. Antsiranana]: Ankarana RS , N of Ambilobe, 12°56'S 49°07'E, 100–300 m, 20.III.1993, fl., Andrianantoanina & Du Puy 27 ( MO); Ankarana, Sentier Botanique , 17 km NE de Mahamasina , 12°50'47"S 49°06'18"E, 82 m, 17.I.2002, fl., De Block et al. 1277 (G, MO). Reg. Melaky [Prov. Mahajanga]: Tsingy du Bemaraha (9e Réserve), 1932–1933, fl., Leandri 356 ( MO, P [3 sheets]) .

Figures

Fig. 7. – Homalium pseudoracemosum Appleq. A. Flowering branch; B. Portion of inflorescence; C. Flower. [Service Forestier 16408, P] [Drawings: R.L. Andriamiarisoa]

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