Homalium ranomafanicum Appleq.

Wendy L. Applequist, 2016, Revision of the Malagasy species of Homalium sect. Eumyriantheia Warb. (Salicaceae), Candollea 71 (1), pp. 33-60 : 55

13. Homalium ranomafanicum Appleq. , spec. nova

( Fig. 2 E, 5).

Typus: Madagascar. Prov. Fianarantsoa: Ranomafana National Park , parcelle 3, S of National Road 25 at 7 km W of Ranomafana town, 21°15’30’’S 47°25’00’’E, 953 m, 900-1100 m, 15.XII.1994, fl., Randrianasolo & Bernardin 209 (holo-: MO-6669934 ! ; iso-: BR!, CAS!, G!, K!, L!, TAN, USMS).

Homalium ranomafanicum Appleq. differs from H. maringitra H. Perrier in having larger, broadly obovate (to obovate or broadly elliptical) leaves with revolute, untoothed margins bearing 0 to 2 basal glands, paniculate inflorescences.

Tree to 20 m tall, 25 cm dbh; large twigs grayish brown; young twigs dark brown, glabrous; stipules broadly deltoid to ovate, 0.5-1 mm, glabrate. Leaves alternate (to subopposite); petiole (3-) 5-8 mm, glabrous; blade broadly obovate (to obovate, broadly elliptical), 4-7.3 × 2.1-5.1 cm; base convex (to cuneate or rounded); apex rounded (to shallowly emarginate or roundedcuspidate); margins revolute, sometimes strongly, with 0 to 2 basal glands just inside margin; abaxial surface glabrous, drying a warm medium brown; adaxial surface glabrous, drying dull to pale or greenish brown. Inflorescences paniculate, often with multiple well-developed proximal branches and with many flowers borne in small clusters on short branches, lateral mostly near twig apices, (3.3-) 8-16 cm, sparsely pubescent proximally, the distal branches moderately minutely pubescent; peduncle 0.6-5.6 cm, sturdy; pedicel 1-2(-2.5) mm, at least moderately minutely pubescent; bracts deltoid to ovate, 0.5-1.2 mm, short-pubescent; bracteoles broadly deltoid, 0.3-0.6 mm, short-pubescent. Flowers: sepals 4, broadly oblong to oblong with rounded apex, 1.4-2.6 mm, abaxial surface sparsely minutely pubescent; calyx cup funnelform, moderately minutely pubescent; sepal glands irregularly oblong to trapezoid, (0.8-)0.9-1.2(-1.5) × 0.6-0.7 mm, upper surface densely short-pubescent; petals white, obovate with a narrow base and rounded apex, 3.6-5.2 × 1.5-2.3 mm, about twice as long as sepals, abaxial surface minutely pubescent especially at base and in center, adaxial surface glabrous; filaments 1.7-2 mm, glabrous; anthers 0.2-0.3 mm; ovary nearly flat-topped at anthesis, short-pubescent; styles 4, 1.5-2.4 mm, short appressed-pubescent on fused basal portion. Seeds not seen.

Distribution, ecology and conservation status. – Homalium ranomafanicum is native to mid-elevation southeastern humid forest. The type collection, made over two decades ago, is from the national park of Ranomafana. No further collections have been seen, though thousands of specimens have been collected from Ranomafana. It is thus likely that this represents a very rare species. However, given the lack of knowledge regarding this species and the fact that its known habitat is relatively well protected, a preliminary conservation status assessment of “Data Deficient” [DD] seems most conservative.

Notes. – The type collection of H. ranomafanicum is the only known collection of its kind from the very well-collected site of Ranomafana National Park. It is notable for having broadly obovate leaves, long panicles with well-developed branches, and small 4-merous flowers with short pedicels, very short sparsely pubescent sepals, and densely pubescent sepal glands. Homalium ranomafanicum is likely to be closely related to H. maringitra and the newly described H. dorrii , which share small flowers with mostly sparsely pubescent sepals and densely pubescent sepal glands. It seems most similar to H. maringitra , which is known from mid-elevation humid forests much farther north, and which similarly has petals almost twice as long as the sepals. The leaves of H. maringitra are usually smaller, or at least narrower, and mostly elliptical rather than obovate; its leaf margins are toothed or wavy with multiple glands, its inflorescences racemose or racemiform, and its pedicels and sepals frequently longer than those of H. ranomafanicum . Homalium dorrii has narrower leaves and longer sepals, so that the petals only modestly exceed the sepals (see Fig. 2 A and 2E for a comparison). The only species of sect. Eumyriantheia previously known from southeastern midelevation humid forest is H. oppositifolium , which differs from H. ranomafanicum in numerous characters (e.g., its leaves are mostly elliptical, inflorescences racemose, sepals 5-6 in number and longer both absolutely and relative to the petals, and abaxial surfaces of the sepals and petals densely pubescent).

Figures

Fig. 2. – Flowers of newly described species of Homalium sect. Eumyriantheia Warb. A. Homalium dorrii Appleq.: flowers and nearly mature fruit with single seed; B. Homalium pseudoboinense Appleq.: abaxial surface of perianth; C. Homalium pseudoboinense: open flower; D. Homalium randrianasoloi Appleq.; E. Homalium ranomafanicum Appleq.; F. Homalium schatzii Appleq.: open flower; G. Homalium schatzii: abaxial surface of perianth.