Homalium micranthum (Boivin ex Tul.) O. Hoffm., Sert. Pl. Madagasc.

Applequist, Wendy L., 2018, A revision of the Malagasy species of Homalium sect. Blackwellia (Salicaceae), Candollea 73 (2), pp. 221-244 : 236-238

10. Homalium micranthum (Boivin ex Tul.) O. Hoffm., Sert. Pl. Madagasc. : 18. 1881.

, ≡ Blackwellia micrantha Boivin ex Tul. in Ann. Sci. Nat. Bot. ser. 4, 8: 63. 1857.

Lectotypus (first step designated by SLEUMER, 1973: 263; second step designated here): MADAGASCAR. Prov. Antsiranana: Île Nossi Bé , 9.XII.1840, fr., Pervillé 389 ( P [ P04704026 ]!; isolectotype: K [ K000231493 , K000231494 ] images seen, P [ P04704030 , P04704025 ]!, TAN [ TAN000588 ] image seen) .

Tree to 25 m, 70 cm dbh; bark grayish, platanoid; young twigs glabrous or minutely (to short-)pubescent. Leaves elliptical to oblong-elliptical or narrowly oblong (occasionally somewhat obovate to oblanceolate or ovate to lanceolate), (2.4–)3.7– 9.5 × 1.3– 3.4 cm; petiole (1 –)2– 5(–6) mm; base convex (rounded, cuneate); apex acuminate (rounded, acute, cuspidate); margins serrulate to crenate-serrulate on apical half, with glands elongated, at or above tooth apex, often producing exudate; adaxial surface drying dark brown to blackish (greenish), abaxial surface brown (olive). Inflorescences racemose, lateral, often paired (sometimes very numerous), (1.8–) 2.5–10 cm, short-pubescent (in South villous); flowers pedicellate with pedicels (0.2–)0.4 – 1.6(– 2.5) mm; bracts lanceolate to ligulate or ovate, 0.3 – 1.3(– 2) mm. Flowers (6)7(8)-merous; calyx tube funnelform with base broadening in fruit, sparsely pubescent (sometimes becoming glabrous); sepals more or less ligulate with acute apex, 1.0– 3.8 mm; petals ligulate to spatulate (narrowly elliptical) with acute apex, 1.4–4.4 mm; sepals and petals white to pale or yellowish green, sometimes red-tinged, or pink (probably only in fruit), accrescent, moderately to slightly longer than calyx tube, usually mostly ascending in flower, sometimes fully reflexed in early flower, commonly becoming irregularly spreading to reflexed in fruit, ciliate, both surfaces sparsely pubescent to glabrous; sepal glands pubescent; filaments (0.9–) 1.3–2.7 mm, glabrous (sparsely pilose); ovary pubescent; styles 4, 1.4–2.6 mm, pubescent at base.

Vernacular names and use. – “Fotsiakara” (Service Forestier 16265 [Taisaka dialect]); “Janganito” (Antilahimena 211, Birkinshaw & Antilahimena 540, Réserves Naturelles 3004, Service Forestier 7718); “ Janganito malandy” (Madiomanana et al. 279, Service Forestier 3881, 11074, 13108); “Zanganito” (Réserves Naturelles 9398); “Zanganito malandy” (Service Forestier 11514).

Wood of H. micranthum is used for construction (Service Forestier 16265).

Distribution, ecology and conservation status. – Homalium micranthum is mostly native to northeastern Madagascar, primarily from Antsiranana; it has been reported on laterite. As presently circumscribed, it includes several specimens from eastern and southeastern Madagascar. As such, it has a large range and has been collected in several protected areas (Lokobe, Montagne d’Ambre, Manombo, Masoala, Manongarivo) so its conservation status must be estimated as “Least Concern” [LC].

Notes. – Most collections of H. micranthum are from northeastern Madagascar, almost all from Antsiranana. Several collections outside Antsiranana have previously, or now for the first time, been tentatively identified as having affinities to H. micranthum . The geographic range of these specimens is suspiciously broad, but for the most part, though they are all at the extreme of the species’ morphological range in at least one or two characters, they are not clearly distinguished from it. Specimens from eastern littoral forests have moderately villous inflorescences, in contrast to the more usual short-pubescent inflorescences. The few specimens from the southeast (Prov. Tulear) are of particular interest: mature leaves are not available for all, but they seem to share an unusual leaf shape (obovate, rounded-cuspidate apex, sometimes cuneate base) and to have the calyx tube normally, rather than rarely, glabrate at maturity. The bark description in the label data of Service Forestier 16265 from Fianarantsoa is somewhat inconsistent with descriptions from Antsiranana. Since the floral morphology of these specimens is unremarkable, they are not segregated at this time, but the availability of more material in future might allow them to be recognized as distinct.

Among the atypical specimens of H. micranthum is Perrier de la Bâthie 18374, originally a syntype of H. viguieri H. Perrier. This specimen seems to fit better in H. micranthum than in H. viguieri , primarily due to its long and relatively narrow petals; its relatively large, short-acuminate leaves and mostly shortpedicellate flowers are more typical of H. micranthum , though not totally unknown in H. viguieri . It has slightly longer bracts than typical of H. micranthum and unusual sparsely pilose filaments, but otherwise resembles typical H. micranthum . Further investigation of any surviving population in the area would be desirable.

Another problematic specimen is Service Forestier 23946 (P), from coastal Fianarantsoa between Farafangana and Manombo. This collection resembles H. micranthum from the same area, with some unexpected characters; in particular, the sepal glands are glabrous. It may be a hybrid involving H. micranthum and a species with glabrous glands, most plausibly H. axillare (which is not known from that area, but which has a sufficiently wide range that its presence would not be surprising).

The protologue of Blackwellia micrantha cited Pervillé 389 and Boivin 2125. The latter collection provided the holotype of the simultaneously published B. eriantha Tul. A portion of the material of Pervillé 389 at P was wrongly marked in the herbarium with a Boivin label and “2125”. The real Boivin 2125 is very different in appearance, as Homalium micranthum and H. erianthum are not at all confusable. It may be presumed that Tulasne intended to quote label data, including the misused number, and did not intend to include the real Boivin 2125 in Blackwellia micrantha . Therefore, Pervillé 389 constitutes the only original material. SLEUMER (1973) stated that the “ holotype ” was “Pervillé Herb. 389 in Herb. Boivin 2125” at P, with an isotype at K. This would constitute an effective first- step lectotypification, but there are actually three probable duplicates of Pervillé 389 at P, from which one still needs to be selected as lectotype.

The sheet chosen here, [P04704026], is preferred because it is the largest fragment and also the least susceptible to confusion, since it is marked only with a printed “Pervillé 1841” label and a handwritten “No. 389”. The second sheet, [P04704030], bears a printed “Boivin 1847–1852” label and hand-marked “no. 2125”, as well as handwritten labeling that says “Pervillé leg. et ... comm, sub n. 389” and also “2125. Nossi-bé. Bernier comm. 1846” [i.e., before the date of Boivin’s voyage]. The third sheet, [P04704025], bears only the Boivin label and herbarium number, with a fragment packet marked “ Blackwellia micrantha Tul. ”; it is Homalium micranthum and can be presumed to be unlabeled material of Pervillé 389.

Selected material examined. – MADAGASCAR. Prov. Antsiranana: Nosy-Be , RNI Lokobe , 13°24'30"S 48°18'15"E, 0–50 m, 7.XII.1994, fl. & fr., Antilahimena 211 ( MO, P) ; Nossi-be , env. d’Ambatozandry , 50–250 m, 14.XII.1967, fr., Bernardi 11867 ( P) ; Réserve Naturelle Intégrale No. 6 , Lokobe , 5 km SE of Hell Ville, 13°25'S 48°18'E, 100 m, 28.XI.1992, fl., Birkinshaw 193 ( MO, P) ; Ramena valley, fkt. Antsahabe , 13°49'30"S 48°46'59"E, 500 m, 10.X.1998, fl., Birkinshaw & Antilahimena 540 ( MO, P) ; Ambahatra cours supérieur , 13°59'S 48°26'E, crête entre les deux bras de l’Ambahatra , 24.V.2000, fr., Gautier & Rakotomamonjy 3649 ( MO, P) ; Nosi-be , IX.1879, fr., Hildebrandt 3178 ( P [2 sheets]) ; Ampasindava, forêt d’Andranomatavy , 13°39'42"S 47°58'41"E, 615 m, 30.XI.2009, fr., Madiomanana et al. 279 ( P) ; Parc National de Montagne d’Ambre , 12°32'S 49°11'E, 990–1100 m, 16–20.XI.1992, fl., Malcomber et al. 1805 ( MO, P) ; Daraina, forêt d’Antsahabe , 13°12'53"S 49°33'19"E, 796 m, 14.I.2004, fr., Nusbaumer 961 ( MO, P) ; vallée du Sambirano , I.1909, fl., Perrier de la Bâthie 4591 ( P) ; H[aut]e Mananjeba , 300 m, IV.1913, fl., Perrier de la Bâthie 6702 ( P) ; Daraina, forêt de Binara , 13°14.06'S 49°37.31' E, 300 m, 31.III.2004, fl. & fr., Ranirison 552 ( MO, P) ; Marotongoza , Nossi-Bé , 12.III.1957, fr., Réserves Naturelles 9398 ( P) ; Ambodimangatelo, Ambanja , 12.X.1951, fr., Service Forestier 3880 ( P) ; Ambaliha, Ambanha , 18.X.1953, fr., Service Forestier 7718 ( P) ; Maromiandra, Ambanja , 6.X.1954, fl., Service Forestier 11074 ( MO [2 sheets], P) ; massif de l’Antsatrotro ( Manongarivo ), 900 m, XI.1954, fl., Service Forestier 11514 ( P [2 sheets]) ; Bekolosy, Ambanja , 17.XI.1954, fl., Service Forestier 13108 ( P) ; massif de la Montagne d’Ambre , rive droite de la riv. des Makis entre la Station des Roussettes et la grande cascade , 18–20.XI.1958, fr., Service Forestier 20039 ( MO, P) ; Prov. de DiegoSuarez, s.d., fr., Ursch 205 ( P) . Prov. Fianarantsoa: Distr. Farafangana, cTOn Ihorombé , Manombo , 31.V.1956, fr., Service Forestier 16265 ( P) . Prov. Toamasina: Ambatovola , Vohitra , 700 m, I.1928, fl. & fr., Perrier de la Bâthie 18374 ( P) ; [ Masoala ] Peninsula , trail just above Antalavia River on S bank , 1–2 km from coast, 15°45'S 50°02'E, 50–100 m, 19.II.1988, fl. & fr., Schatz et al. 1922 ( MO, P) . Prov. Toliara: Fort-Dauphin , s.d., fl., Cloisel 188 ( MO, P) ; près de la riv. Antorendrika avant Belavenona , 24°52'S 47°07'E, 0–20 m, 22.III.1989, fl., Rabevohitra 1773 ( MO, P) ; Fkt. Ambandrika, Analavinaky S8 , 24°46'29"S 47°08'57"E, s.d., fl. & fr., Randriatafika & Rabenantoandro 412 ( MO, P) .