Homalium phillipsonii Appleq., 2020

Applequist, Wendy L., 2020, A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar, Candollea 75 (2), pp. 245-268 : 258-260

7. Homalium phillipsonii Appleq. , sp. nov.

( Fig. 6 ).

Holotypus: MADAGASCAR. Reg. Atsimo-Atsinanana [Prov. Toliara]: near Sakaraha, forêt de Zombitsy , 22°52'S 44°31'E, 750 m, 6.I.1989, fl., Phillipson 3095 ( MO-3762461 !; iso-: G [ G00341926 ] image seen, P [ P04679124 ]!, TAN) .

Homalium phillipsonii Appleq. differs from H. albiflorum (Boivin ex Tul.) O. Hoffm. in having pilose indument on all parts, leaves sometimes narrower, with strongly prominent secondary veins, sometimes with apparent small domatia in axils, and often asymmetrical apices, and larger anthers.

Tree to 15 m tall or shrub; bark caducous in plaques; twigs pale (dark) brown when young, becoming dark to grayish, pilose. Leaves elliptical to obovate, oblong-elliptical or narrowly elliptical (to oblanceolate), (4–)5.5–14 × (1.8–) 2.4–6 cm, relatively thin-textured; margin shallowly crenate to crenateserrulate; base convex (to rounded); apex short-acuminate to cuspidate (long-acuminate), often asymmetrical at tip, to acute (obtuse, emarginate, rounded-obtuse); both surfaces pilose especially over veins, more sparsely short-pilose adaxially, drying green or brown, the adaxial surface darker (seldom dark grayish); secondary veins strongly prominent, sometimes apparently with small domatia in axils; petiole sometimes red, (5–) 7–14 mm, pilose. Inflorescences racemose, (2.5–)5–12(–16.5) cm; peduncle 1–3.5 cm; rachis short-pilose; flowers 2–3(4) per node; pedicels 0.5– 2 mm, pilose. Flowers 5-merous, white; sepals obovate-oblong to oblong-elliptical or narrowly oblong, 0.9–2.4 mm, short-pilose to appressed-pubescent on outer surface and apical part of inner surface, margins ciliate; sepal glands broadly elliptical (orbicular), 0.4– 0.7(– 0.8) × 0.4– 0.6 mm; calyx cup pilose; petals obovate with a narrowed base to oblanceolate, 1.5–8 mm, strongly accrescent, sparsely short-pubescent on both surfaces, margins ciliate; filaments 0.7–1 mm; anthers broadly elliptical, 0.35 mm high.

Etymology. – Homalium phillipsonii is named for Peter B. Phillipson, collector of the type, to honor his many contributions to the botany of Madagascar.

Vernacular names. – “Lalimpitonala” (Service Forestier 4570); “Lalipitonala” (Service Forestier 4989); “Lalipitonantro” [?] (Service Forestier 3401); “Lalipotonala” (Service Forestier 2818).

Distribution, ecology and conservation status. – Homalium phillipsonii as herein described is native to the Atsimo-Andrefana region of southwestern Madagascar ( Fig. 2 ). [As noted below, there are similar populations in northern Madagascar, but the status of these is doubtful]. It occurs in dry deciduous forest and bush, on sand and rocky limestone substrates. Based on historical collections, the EOO is estimated as 11,806 km ², and the AOO as 72 km ². It appears that more than ten distinct populations have existed. However, in recent decades all collections but one (Razakamalala 6111) have been made in the protected area of Zombitsy. The vast majority of the habitat is unprotected, has suffered severe damage since the time when historical collections were made (with all woody species suitable for use as charcoal virtually extirpated in many areas), and continues to be subject to ongoing anthropogenic damage.

Therefore, it is considered very likely that some of the historical populations are now extinct, and that the species should be assessed as “Vulnerable” [VU B2ab(iii)].

Notes. – Homalium phillipsonii is most readily distinguished from H. albiflorum s.str. by the pilose indument of its leaves, twigs, petioles, and portions of the calyx. In H. albiflorum , the pedicels and calyx are occasionally pilose but the leaves, twigs, and petioles, though rarely pubescent, are not pilose. Homalium phillipsonii has more strongly prominent secondary veins than any related species, and more frequently has small structures interpreted as domatia. The inflorescences also seem subjectively to appear thicker and less pendent than those of H. albiflorum , and the anthers are larger and narrower than usual for that species (whose morphology is variable).

A few specimens that key out as H. phillipsonii , noted below as “ incertae sedis ”, are from much farther north, even from the extreme north. There are no specimens of H. phillipsonii known from the intervening regions, so if those populations were H. phillipsonii the species would have a highly disjunct distribution. These sometimes have a sparser indument on various parts than typical H. phillipsonii and might be viewed as transitional forms between H. phillipsonii and H. albiflorum , which does occur in that range. However, material of H. albiflorum from the southernmost portion of the distribution of that species (the regions of Menabe and Melaky) does not appear to intergrade with H. phillipsonii , farther to the south, at all. It is therefore questionable whether gene flow between the species is possible. The northern populations may well be genetically distinct, although they are not strongly distinguished morphologically; further collections from the region might help to resolve their status.

Paratypi. – MADAGASCAR. Reg. Atsimo-Andrefana [Prov. Toliara]: Manasoa Tanosy, 11.I.1913, fl., Afzelius s.n. ( MO [2 sheets], P) ; Andoharanomaitso, Parc de Zombitse , partie SE, 22°54'22"S 44°40'22"E, 800 m, 25.XII.2004, fl., Andriamihajarivo et al. 540 ( MO) ; Parc National de Zombitse , NW du village de dika , lieu dit Poakafo, 22°46'09"S 44°40'15"E, 531 m, 10.IV.2006, fr., Andriamihajarivo et al. 921 ( MO, P) ; Sakaraha, II.1956, fl., Bosser 9111 ( MO, P) ; Tsarasao S de Sakaraha , 14.II.1970, fl., Bosser 19913 ( P) ; Baie de St. Augustin (Tulear), 8.II.1957, fl., Descoings 2406 ( MO) ; Basse vallée du Fiherenana , 50–200 m, XI.1933, fl., Humbert 11557 ( G, P [2 sheets]) ; Bassin moyen du Fiherenana entre Lambomakandro et Sakaraha, 400 m, 10.XII.1946, fl., Humbert 19683 ( G, P) ; Gorges du Fiherenana entre Beantsy et Anjamala, 30–300 m, 16–19.I.1947, fl., Humbert 19920 ( P) ; Plateau au S des gorges du Fiherenana entre Andranohinaly et Andranovory, 300–400 m, 3–4.II.1947, fl., Humbert 20112 ( P) ; forêt de Zombitsy (entre Ranohira et Sakaraha), III.1960, fl., Keraudren 484 ( P [2 sheets]) ; 20 km S de Sakaraha , Tsaramasao, III.1970, fl., Morat 3503 ( MO, P [6 sheets]) ; Zombitsy, 1 km N du village d’Andranomaintso , 22°53'23"S 44°38'36"E, 600–700 m, 3.II.1999, fr., Randrianaivo et al. 312 ( MO, P) ; Fkt. Betorabato, Ambalamanga, forêt Akolitsika , 21°40'22"S 44°59'36"E, 286 m, 21.I.2011, fl., Razakamalala 6111 ( MO) ; rte Tulear Sakaraha, 23.II.1949, fl., Service Forestier 517 ( P) ; Analamary, Sakaraha, 22.I.1951, ster., Service Forestier 2818 ( P) ; Andranovory, Tuléar, 19.III.1951, fr., Service Forestier 3401 ( P) ; Lambomakandro, Tuléar, 23.I.1953, fl., Service Forestier 4570 ( P) ; Soaserana, Sakaraha, 21.II.1952, fl., Service Forestier 4989 ( P) ; forêt Anadabovalo , Ambohimahavelona, Tuléar , 27.I.1955, fl., Service Forestier 13064 ( P) ; forêt d’Hera [Ihera], au N de Mitia dans le haut bassin de l’Ilona (au NE du massif de l’Analavelona), 600–700 m, 16.XII.1962, fl., Service Forestier 22216 ( P).

Specimens incertae sedis: MADAGASCAR. Reg. Boeny [Prov. Mahajanga]: Bemazava, près de l’embouchure de la Mahavavy ( Ambongo ), VI.1903, fl., Perrier de la Bâthie 2264 ( P) ; forêt de Bekapika , sur le plateau d’Antanimena (Boina), 12–14.XI.1957, fl., Service Forestier 18432 ( P). Reg. SAVA [Prov. Antsiranana]: Daraina, forêt de Ambilondomba , 13°09'S 49°38'E, 480 m, 27.I.2004, fl., Ranirison et al. 323 ( MO, P). Reg. Sofia [Prov. Mahajanga]: distr. Analalava, forêt d’Ambondro-Ampasy (Exploitation Loyseau), 29.X–3.XI.1958, fl., Service Forestier 18835 ( MO, P).

Figures

Fig. 6. – Homalium phillipsonii Appleq. A. Flower; B. Flowering branch; C. Inflorescence; D. Detail of leaf venation. [Phillipson 3095, TAN] [Drawings: R.L. Andriamiarisoa]

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