Homalium retusum (Blume) Wassel & Appleq., 2020

Wassel, Anna C. & Applequist, Wendy L., 2020, A revision of Homalium sect. Nisa (Salicaceae) endemic to Madagascar, Candollea 75 (1), pp. 1-23 : 15-16

9. Homalium retusum (Blume) Wassel & Appleq. , comb. nov.

≡ Nisa retusa Blume, Mus. Bot. Lugd. -Bat. 2: 28. 1856.

Lectotypus (designated here): MADAGASCAR. Reg. Analanjirofo [Prov. Toamasina]: Ile Ste. Marie , VIII–IX, fl., Bernier 173 ( L [ L0010974 ]; isolecto-: K [ K000231491 , K000231492 ] images seen, L [ L0010975 , L0010976 ] images seen, P [ P00418083 , P00418084 , P00418085 ]!, TAN [ TAN000593 ] image seen) .

= Homalium scleroxylon (Tul.) Baill. in Bull. Mens. Soc. Linn. Paris 1: 575. 1886. ≡ Nisa scleroxylon Tul. in Ann. Sci. Nat., Bot. sér. 4, 8: 69–70. 1857. Lectotypus (first step designated by SLEUMER, 1973: 299; second step designated here): MADAGASCAR. Reg. Analanjirofo [Prov. Toamasina]: Ile Ste. Marie , VIII – IX, fl., Bernier 173 ( P [ P00418085 ]!; isolecto-: K [ K000231491 , K000231492 ] images seen, L [ L0010974 , L0010975 , L0010976 ] images seen, P [ P00418083 , P00418084 ]!, TAN [ TAN000593 ] image seen). Syntypus: Galdich. [Gaudichaud] 296 [in phytotheca Jalbertiana] (not located) .

Tree 6–7 m tall, 10 cm dbh; twigs gray to medium brown, glabrous, leafing internodes 1.6–3.5(–4.5)mm diam.; stipules 2– 6 mm, sparsely ciliate. Leaves obovate to broadly elliptic, (5–)7–16 × 3.5–9 cm (unusually small leaves sometimes subtending inflorescences); base cuneate to convex; apex rounded to retuse or cuspidate; margin entire, rarely slightly crenulate, glands small; secondary veins (5–)6 –9(– 14) per side; both surfaces glabrous, drying light to medium brown on adaxial surface and darker on abaxial surface; petiole glabrous, (10–) 15–30 mm. Inflorescences paniculate, axillary, 8 –12 cm; rachis short-pubescent; bracts and bracteoles 1–3 mm, usually ciliate, otherwise glabrous to sparsely pubescent; flowers mostly paired with 2 per bract. Flowers 5–6-merous, white or yellow; sepals obovate at anthesis becoming oblanceolate, 4–8(– 9) mm, adaxial and abaxial surfaces glabrous; sepal glands glabrous; petals oblong-ovate, 1.5–3 mm, adaxial surface usually pubescent apically, basally glabrous, abaxial surface glabrous except often pubescent at extreme apex, margin usually ciliate; filaments glabrous, 1.2–1.9 mm; anthers (0.3–) 0.35–0.45 mm; styles (0.7–)1.2–1.7(–2) mm.

Distribution, ecology and conservation status. – Homalium retusum is found near the eastern coast in the northern part of Madagascar at low elevations. Few specimens are known, suggesting that this is an uncommon to rare species. Only five clearly distinct subpopulations have been recorded (Ile Ste.-Marie in Analanjirofo, Foulpointe and Ambila-Lemaitso in Atsinanana, and Anjana and Andempona in SAVA). The Extent of Occurrence (EOO) is calculated as c. 9847 km ² and the Area of Occupancy (AOO) as 28 km ². Much of the habitat is subject to ongoing anthropogenic damage, especially in view of its relative accessibility. Therefore, a preliminary assessment of its conservation status is Endangered [EN B1ab(iii)+2ab(iii)].

Vernacular names and use. – “Hazombato” (Service Forestier 2587); “Longotra” (Service Forestier 9646); “Marangué Touditch” (Bernier 173, Chapelier s.n.); “Voapak” (Humblot 63); “Zana” (Service Forestier 4918); “Zanakanivato” (Service Forestier 2597).

Wood is good for construction (Bernier 173).

Notes. – Homalium retusum has previously been lumped into H. nudiflorum s.l. ( SLEUMER, 1973), which as herein circumscribed, differs in having smaller, narrower, shorterpetioled leaves; its inflorescences are usually racemose, not over 9 cm, glabrous or sparsely pubescent, with flowers borne singly. Homalium retusum most closely resembles H. pachycladum : both have relatively large leaves, paniculate inflorescences, and flowers with glabrous sepals and near-glabrous petals. Homalium retusum is known only from low-altitude and littoral forests, while H. pachycladum occurs farther inland and at much higher elevations. Homalium pachycladum has elliptic to obovate (or rarely ovate) leaves with shorter petioles (6–15 mm) and flowers all borne singly; its twigs seem usually to be thick, giving a robust appearance. Another inland species with large leaves, H. confertum , is distinguished by having usually elliptic to oblong-elliptic leaves with a serrate to crenate margin, racemose inflorescences with flowers borne singly, and petals densely pubescent on most of both surfaces.

The history of the names applying to this species resembles that of Homalium planiflorum (Boivin ex Tul.) Baill. ( Blackwellia planiflora Boivin ex Tul. ) versus Blackwellia gracilis Blume (see APPLEQUIST, 2017, 2018b), but without disruptive nomenclatural consequences. Blume published Nisa retusa based on material of Bernier 173 a year before Tulasne published N. scleroxylon based mostly on the same collection. Blume specified that his name was based only on material sent from P to L. That material was described in the protologue ( BLUME, 1856 –1857: 28) as “Nomine Asteropeia et Mourangia Touditsch ex Herb. Mus. Paris. mecum benevole communicata.” Three sheets at L bore labels initially marked “ Asteropeia [or Asteropeja] multiflora ” then “ Mourangia [or Morangia] touditch ” (a vernacular name, though not identified as such on those sheets); Blume later added “ Nisa retusa ” in the top margins. Much more recent pink typed labels identify these sheets as being type material of N. scleroxylon , “leg. Bernier 173 ”.

One year later, Tulasne published N. scleroxylon , citing “Bernerii herb., n. 173; Galdich. herb., n. 296, in phytotheca Jalbertiana” ( TULASNE, 1857: 70). These are Latinizations for Bernier and Gaudichaud-Beaupré respectively. Although Tulasne presumably used only those duplicates of Bernier 173 to be found in France, he did not say so. The protologue ( TULASNE, 1857: 70) further states: “ Marangue-Touditch (1), auctore Bernerio, vernaculare audit…”, explaining the labeling seen, and apparently misinterpreted, by Blume. Three duplicates of Bernier 173 exist at P; two were labeled as having the vernacular name “ Maranguá touditch ” and one had initially been labeled “ Asteropeia ”. Though the sheets sent to L were not initially labeled as Bernier 173, they can be confidently assigned to that collection.

SLEUMER (1973: 299) referred to Bernier 173 (L) as the “ holotype ” of Nisa retusa and to Bernier 173 (P) as the “ holotype ” of Nisa scleroxylon . For N. retusa , the original material was already restricted to the three sheets at L, which are syntypes, and Sleumer made no choice between them. The sheet that appears most complete is here chosen as a lectotype. For N. scleroxylon , Sleumer’s statement constitutes a first-step lectotypification (Art. 9.17 of ICN; TURLAND et al., 2018). This action means that N. retusa and N. scleroxylon are not nomenclatural synonyms, since their types are different specimens, even though they are from the same gathering. The best of the sheets at P is here chosen as a second-step lectotypification.

Additional material examined. – MADAGASCAR. Reg. Atsinanana [Prov. Toamasina]: Foulpointe ?, s.d., fl., Chapelier [ Herb. Boivin ] s.n. ( P [2 sheets]); Foulpointe , Morarano , Andohanakoho , 17°41'52"S 49°27'28"E, 34 m, 9.III.2005, fl., Lehavana et al. 304 ( MO, P) ; Foulpointe , forêt d’Analalava , 17°42'00"S 49°26'00"E, 35 m, 19.V.2004, fl., Randrianarivelo et al. 2 ( MO, P) ; Sahapanpana , Foulpointe , 20.VI.1950, fl., Service Forestier 2587 ( P) ; Ambila-Lemaitso , 1.II.1952, fr., Service Forestier 4918 ( P) ; Ambila-Lemaitso , 27.IV.1954, fl., Service Forestier 9646 ( P) . Reg. SAVA [Prov. Antsiranana]: W de Nosiarina, sommet d’Anjana , 14°12'23"S 50°04'26"E, 190 m, 29.VIII.2007, fr., Andriamihajarivo et al. 1341 ( MO) ; Antalaha , Andempona , 13.VI.1950, fl., Service Forestier 2597 ( MO, P) . Sine loco: Madag. bor ., Andahoul , s.d., fr., Humblot 63 ( P) .