Homalium megaphyllum Appleq., 2020

Applequist, Wendy L., 2020, A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar, Candollea 75 (2), pp. 245-268 : 256

6. Homalium megaphyllum Appleq. , sp. nov. ( Fig. 5 ).

Holotypus: MADAGASCAR. Reg. DIANA [Prov. Antsiranana]: Behefaka, Anjahana , 13°21'32"S 49°10'10"E, 123 m, 5.VI.2005, fr., Hong-Wa et al. 296 ( MO-6175072 !; iso-: G [ G00341931 ] image seen, P [ P04734804 ]!, TAN).

Homalium megaphyllum Appleq. differs from H. leucophloeum (Tul.) Baill. in its much larger, usually elliptical to oblongelliptical leaves with usually subentire margins, inflorescences often cauliflorous on twigs below leaves, and flowers often short-pedicellate.

Tree to 20 m tall, 30 cm dbh; twigs dark brown, glabrous. Leaves elliptical to oblong-elliptical (narrowly elliptical, ovate), 13– 35 × (5–) 5.7 – 11.5 cm, relatively thin-textured (moderately thick); margin subentire, often slightly undulate; base rounded to convex or somewhat oblique; apex cuspidate to short-acuminate or acute (rounded, emarginate); both surfaces glabrous, drying brown or green abaxially, dark brown to blackish (seldom greenish) adaxially; secondary veins slightly prominent; petiole sometimes red, (11–)13–20(–29) mm, glabrous. Inflorescences often mostly cauliflorous on twigs below leaves, racemose, (4.5–)8–15(– 23) cm; peduncle 0.3–1.3(– 3) cm; rachis glabrous (short-pubescent); flowers (1)2 –4 per node; pedicels 0.5–1 mm, short-pubescent, or flowers sessile. Flowers 4-merous, white; sepals oblong to somewhat obovate, 1.3–3.5 mm, glabrous except margins short-ciliate; sepal glands suborbicular, 0.5–0.6 × 0.5 mm; calyx cup sparsely pubescent; petals narrowly obovate, 3.5– 7 mm, moderately accrescent, glabrous, margins not ciliate; filaments 0.6–0.9 mm; anthers transversely elliptical, c. 0.3 mm high.

Etymology. – Homalium megaphyllum is so named for its exceptionally large leaves.

Vernacular names. – “Hazoadala” (Antilahimena et al. 370, 463, Gautier & Be 2905, Réserves Naturelles 1449, 2954, 4362, Service Forestier 7690, 9293, 13388); “Hazoanolalana” (Service Forestier 3054).

Distribution, ecology and conservation status. – Homalium megaphyllum is confined to northern Madagascar, primarily the DIANA region ( Fig. 2 ). It is frequently reported to occur along the banks of rivers or streams, including seasonal temporary streams, and once to grow in deep red soil. It has been collected in degraded, or secondary, savoka forests.

More than ten probably distinct populations have been collected, and it occurs in the protected areas of Manongarivo, Tsaratanana and Lokobe. Its conservation status is tentatively assessed as “Least Concern” [LC].

Notes. – Homalium megaphyllum is certainly more closely related to H. leucophloeum and H. baillonii than to H. albiflorum s.str., as evidenced by its 4-merous flowers with glabrous sepal and petal surfaces. It has a much larger maximum leaf size than any other species of the section, and is also unique in having most inflorescences borne proximally on mature twigs, rather than in leaf axils.

Paratypi. – MADAGASCAR. Reg. DIANA [Prov. Antsiranana]: Ambato classified forest , river Bevoay , trail to Ankarefo, 13°28'03"S 48°32'22"E, 0–100 m, 28.V.1998, fl., Antilahimena et al. 370 ( G, K, MO, P) ; Tsaratanana Massif , Antsahabe-Mandrizavona , 13°43'12"S –13°48'S 48°39'25"E –48°45'E, 150–750 m, 12.IV.2000, fl., Antilahimena et al. 463 ( BR, G, K, MO, P) ; env. de Maromandia (Kapany), 9.IV.1923, fl., Decary 1676 ( G, P) ; Besinkara, 14°04'S 48°17'E, ch. d’Ambalafary à Ambodisakoana, 350 m, 26.III.1996, fl., Gautier & Be 2905 ( G, MO, P) ; SW d’Ambilobe, 10 m, III.1951, fr., Humbert & Capuron 25589 ( P) ; Vallée de l’Ifasy en aval d’Anaborano, distr. d’Ambilobe Nord, 50–200 m, 31.III.1951, fr., Humbert & Capuron 25880 ( P) ; env. de Mt. Bekolosy , massif de Manongarivo , III.1909, fl. & fr., Perrier de la Bâthie 6718 ( P [2 sheets]) ; presqu’île d’Ampasindava, 13°46'30"S 48°05'35"E, 215 m, 7.V.2012, fr., Rasoanaivo & Tahinarivony 28 ( MO) ; Tsaratanana, rive droite du Sambirano , au delà du village Beangona, 21.V.1948, fr., Réserves Naturelles 1449 ( P [3 sheets]) ; Lokobe, Nossi Be , 22.IX.1952, fl., Réserves Naturelles 4362 ( P [2 sheets]) ; Andrahibo, Ambanja , 16–30.III.1951, fl., Service Forestier 2954 ( P) ; entre Ambatobe et [illegible], distr. d’Ambilobe, 12.III.1951, fl., Service Forestier 3054 ( P) ; Benavony, Ambanja , 25.III.1954, fr., Service Forestier 9293 ( P) ; Manongarivo RS , Anketraka Be, Bas Ambahatra, cours inférieur du bassin-versant de rano Ambahatra (13°55'16"S, 48°27'47"E), 180 m, 22.VII.1998, fr., Wohlhauser & Andrianjaka 60016 ( G, MO, P). Reg. Sofia [Prov. Mahajanga]: Analalava, Bekaraka , env. 40 km S d’Ambanja le long de la RN6, 13°56'09"S 48°12'45"E, 195 m, 21.V.2006, fl., Rakotoarisoa & Andriamahay 436 ( MO) ; Ambodisaina, Ambanja , 17.IX.1953, fr., Service Forestier 7690 ( P) ; Ampondralava, Antsohihy , 25.IV.1955, fr., Service Forestier 13388 ( P). Reg. unknown: sine loco, s.d., fr., Baron 6224 ( P).

Figures

Fig. 5. – Homalium megaphyllum Appleq. A. Flowering branch; B. Flower post-anthesis; C. Inflorescence. [Hong-Wa 296, TAN] [Drawings: R.L. Andriamiarisoa]

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