Polyosma leptorhachis Schulze-Menz ex B.J.Conn & O.K.Paul, 2024

Paul, O. K., Conn, B. J. & Henwood, M. J., 2024, Taxonomic review of Polyosma (Escalloniaceae) in Papuasia, Blumea 69, pp. 54-88 : 78-79

19. Polyosma leptorhachis Schulze-Menz ex B.J.Conn & O.K.Paul , sp. nov. — Fig. 12

Etymology.The specific epithet ( leptorhachis ) of this new species refers to the slender, narrow (lepto­) axis (- rhachis) of the inflorescences.

Polyosma leptorhachis is morphologically similar to P.rigidiuscula (from Australia) with both being shrubby to small trees,but it differs by having a shorter petiole (1–1.5 cm long) and smaller lamina (3.5–8 by 1.5–2 cm), compared to P. rigidiuscula which has a longer petiole (3–8 cm long) and larger lamina (usually 8–15.8 by 2.1–5 cm). — Type: N.A. Vinas & O. Akakavara LAE 59712 (holo LAE [ LAE 228627]; iso A, BISH, BRI [BRI-AQ352765], CANB, E, K, L, M, NSW [NSW2396705]), Papua New Guinea, New Britain, East Nakanai Plateau, 8 Nov. 1975.

Small tree, up to c. 5 m tall. Branchlets glabrous, with scattered white lenticels. Leaves glabrous; petiole 1–1.5 cm long, brown; lamina elliptic, 3.5–8 by 1.5–2.5 cm, coriaceous, drying brown on both surfaces; base cuneate, margin serrate, apex acuminate or attenuate; secondary veins 15–22 on each side and an angle greater than 45° from midrib, regularly looping near margin onto the next secondary vein; tertiary vein weakly percurrent, glabrous, not prominent on abaxial surface. Inflorescence racemose, terminal, <20-flowered; rachis 2.5–3 cm long, glabrous; flowers loosely and evenly arranged; pedicels 2–3 mm long, narrow; bracteoles 1–3 mm long, sparsely hairy. Calyx lobes 1–2 mm long. Corolla buds tubular, 10–15 mm long, green with yellow tinge, turning brown; corolla moderately hairy, remaining tubular at anthesis, except opening with 4 small lobes distally. Fruits ovoid, c. 8 by 5 mm, glabrous, green.

Distribution — Papua New Guinea (Eastern Highlands, Southern Highlands, Western, Central, Milne Bay, New Britain).

Habitat & Ecology — Occurring in montane Beech forests, often on limestone derived soils, at elevations from 2 040 – 2 610 m.

Conservation status — Not endangered.

Additional specimens examined (Paratypes). PAPUA NEW GUINEA, Morobe, Siboma, S.A. James 804 & 805 ( LAE, NSW ); Buso Mountains, K. Rau 611 ( LAE ); Lake Trist, E.E. Henty NGF 29104 (BRI, LAE ); Western Highlands, Mt Oibo, W. Takeuchi 10677 (K, L, LAE ); Eastern Highlands, Okapa, T.G. Hartley 12157 ( LAE ); Daulo Pass, K. Kerenga 154 ( LAE ); Mt Otto, D.B. Foreman, Farley, Short & Hynes NGF 48050 (L, LAE ); Southern Highlands, Mt Ne, Habono, D. Frodin NGF 28355 (K, L); 0.75 miles SE of Lei Camp on track to Ibiwara, D. Frodin NGF 28356 (L); D. Frodin NGF 28485 (L); Ibiwara, D. Frodin NGF 28448 (K, L); Onim, Mt Giluwe, J. Ash ANU 20473 ( LAE ); Kiburu, R. Schodde 1437 (L, LAE ); Hides, W.Takeuchi 19179 ( LAE );Western, Juha South, W. Takeuchi 23115, A. Gambia & T. Jisaka ( LAE ); Central,[Main Range] Above the Gap, 2439 m, C.E. Carr 13758 (L); Main Range NW of the Gap, C.E. Carr 15223 (L); Varirata National Park, D.G. Frodin 8052 ( LAE ); Milne Bay, Goodenough Island, L.J. Brass 25109 ( LAE ); New Britain,Lower slopes of Mt Lululua, P.F. Stevens & Y. Lelean LAE 58215 (BRI, L, LAE ).

Notes — 1. Polyosma leptorhachis is also morphologically like P. brachystachys (from New Caledonia) which is also small, being shrubby to a small tree. Polyosma leptorhachis , P. rigidiuscula and P. brachystachys can be readily distinguished by P. leptorhachis having shorter inflorescences (rachis 2.5–3 cm long), whereas the other two species have longer inflorescences ( P. rigidiuscula – rachis 3–11 cm long, and P. brachystachys – c. 5 cm long).

2. Polyosma leptorhachis is also morphologically similar to P. mucronata and P. subalpina . It is a small tree up to 5 m tall, like P. subalpina (vs shrub up to 1 m tall for P. mucronata ); it occurs at lower elevations, up to 2 600 m (vs P. mucronata which extends to high elevations, up to 3 500 m and P. subalpina at elevations of at least 3 000 m). It can also be distinguished by its elliptic leaf lamina (vs obovate for P. acuminata ), leaf base cuneate (vs acute for P. mucronata and P. subalpina ), and apex acuminate or attenuate (vs the apices are mucronate in P. mucronata and P. subalpina ). The lamina of P. leptorhachis has 15–22 secondary veins on each side of the midrib (vs 7–13 in P. mucronata and 9–15 in P. subalpina ). The inflorescence rachis is usually shorter than the other two species (2.5–3 cm long) and glabrous, whereas the rachis in the other two species is hairy and 5.5–6 cm long ( P. mucronata ) and 1.5–9.5 cm long ( P. subalpina ).

3. Schulze-Menz annotated the collection Carr 13758 (L) as a new species, but this collection is regarded as P. leptorhachis as circumscribed here.

Figures

Fig. 12 Holotype collection of Polyosma leptorhachis Schulze-Menze ex B.J.Conn & O.K.Paul (N.A. Vinas & O. Akakavara LAE 59712; LAE).