Zygogynum sororium (Diels) Vink

Vink, W., 2016, The Winteraceae of the Old World. VIII. Some Zygogynum species from New Guinea, Blumea 61 (1), pp. 41-50 : 49

14. Zygogynum sororium (Diels) Vink — Fig. 1

Zygogynum sororium (Diels) Vink (1985) 54. — Drimys sororia Diels (1916) 245. — Bubbia sororia (Diels) A.C.Sm. (1942) 427. — Type: Ledermann 11661 (B†); neotype here chosen: Ledermann 11898 (holo B).

Tree(let) 3–20 m high. Branchlets rather stout, dark grey-brown. Leaves: petiole 10– 20 mm long, flat above, rounded below, dark brown; blade obovate-oblong, 14–22 by 4.5–9 cm, thin-coriaceous, in sicco light purplish brown below; apex acute to obtusely rounded, base acute and shortly abruptly attenuate; midrib almost flat above, strongly prominent below; secondary nerves at 70–80° with midrib, arcingly joined at some distance from margin, prominulous on either side. On lower leaf surface stomata white, in clusters, or forming a lax labyrinth, not over secondary nerves; oil cells scattered, indistinct. Inflorescences with 5 partial inflorescences, these 6 –11 cm long, with rather stout axes, many-flowered, flowers inserted on axes 2nd or 3rd order; empty bracts below inflorescence unknown; pedicels 1–5 mm long, rather stout. Calyx 2–3- or irregularly lobed, 1–1.5 mm long, rather thin, basally bullate. Petals 8 –12, free, (broad) elliptic to obovate, white, outer ones 5–6 by 3–4 mm, middle ones 5–7 by 2.5–3 mm, inner ones 4–5 by 1–2 mm, apex broadly rounded, inner ones obtuse to acute. Stamens 12–22, 1.3–1.6 mm long; thecae apically touching; connective not prolonged; pollen in tetrads. Carpels 4–5, free, 2–2.5 by 1.3–1.5 by 1.2–1.5 mm; stigma about 2/3 of carpel apex, not descending adaxially; ovules c. 21. Fruitlets unknown.

Distribution — PNG: Schrader Mts.

Ecology — Montane (mossy) forest at 1900–2070 m altitude. Flowering May, June.

Specimens examined. PAPUA NEW GUINEA, East Sepik Prov.,Schraderberg,

Ledermann 11661 (B†), 11898 (B), 2070 m alt., 12141 (B†).

Notes — This species is similar to Z. calothyrsum except for the smaller flowers: petals (4–) 5–7 mm vs 5.5–17 mm; and an often different arrangement of the stomata. In Z. calothyrsum the white stomata on the lower leaf side are mostly in strings, sometimes solitary or in a labyrinth; when the latter is the case, the size of the flowers, if present, is decisive for the identification.

For the time being, this species is upheld, although further studies of the very variable Z. calothyrsum (that includes Z. calophyllum may show that the differences are drowned in the general variability.

Figures

Fig. 1 Carpels, all with ventral side to the left, and at the same magnification. – a. Zygogynum archboldianum; b. Z. bosavicum; c. Z. clemensiae; d. Z. cruminatum; e. Z. cyclopensis; f. Z. ledermannii; g, g'. Z. longifolium; j. Z. megacarpum; h. Z. montanum; i. Z. oligocarpum; k, k'. Z. polyneurum; l. Z. schramii; m. Z. sororium; n. Z. staufferianum; o. Z. umbellatum (a. Brass 12712; b. LAE 58822; c. Clemens 4596; d. LAE 69143; e. Royen & Sleumer 6396; f. Takeuchi 6212; g. Vink BW 8413; g'. Robbins 2004; j. Burley & Ismail 4618; h. LAE 61131; i. Schlechter 16470; k, k'. Jacobs 9489; l. Vink BW 8458; m. Ledermann 11898; n. Balgooy 968; o. Boden Kloss s.n.).