Psychotria apdavisiana W.N.Takeuchi, 2013

Takeuchi, Wayne, 2013, Psychotria apdavisiana sp. nov. (Rubiaceae), a remarkable calciphile from the southern karst of Papua New Guinea, Phytotaxa 153 (1), pp. 51-57 : 51-55

Psychotria apdavisiana W.N.Takeuchi , sp. nov. ( Figs. 1–3 )

Affinis Psychotriae reflexapedunculatae Sohmer sed stipulis majoribus usque ad 18–31 mm longis (nec 5 mm longis) infructescentiis capitatis (nec ramosis) differt.

Type: — PAPUA NEW GUINEA. Western Province: Strickland drainage, Juha South , survey track 1 to sinkhole area, mossy montane forest, 5°53.994'S, 142°26.234'E, 910 m, 21 February 2008, Takeuchi , Gambia & Jisaka 23261 (holotype A!; isotypes K!, LAE!) .

Subshrubs to 0.6 m tall, monoaxial (rarely once-branched). Stems compressed, planate or angulate, 2–4.5 mm wide, pithy; surfaces longitudinally wrinkled, furrowed or not, nigrescent to brunnescent, dull, without lenticels, abscission scars absent; indument velutinous, reddish brown, subpersisting; internodes 2–7.5 cm long. Leaves cauline, 3–5 pairs (or with 1 pair on a side branch), equal, obliquely spreading; stipules ovate, 18–31 × 18–22 mm, parted to the middle, paired, free, persisting, venose, conspicuously thickened at the base, distally papery, bifacially tomentose-lanate, margins glabrescent, apical lobes acute, 9–15 × 3–9 mm; petioles (10–)18–30 × 1–2 mm, planoconvex, striate, black, not articulated, indument as for the stem, hairs caducous on upper side, persisting underneath; leaf-blades chartaceous, narrowly obovate, 16.3–25.2 × 5.9–10.7 cm; base cuneate-attenuate, symmetrical, poorly delimited from the petiole or not; margin entire; apex acuminate (acumen to ca. 2.5 × 1 cm); lamina surfaces adaxially fuliginous, glabrescent, abaxially brunnescent to orange-brown, hirtellous on veins, appressedly hairy between veins; cystoliths linear, discolorously pale, infrequent; domatia absent; venation camptodromous, secondary veins 10–15 per side, at the lamina center with divergence angles of (45–)60–85°, 9–17(–25) mm apart, gradually curved toward margins, only rarely uniting by commissural loops; tertiary (crossing) nerves subscalariform, reticulum irregular, coarsely areolate, obscure or invisible; midribs prominulous on both sides; higher order venation weakly raised or planate above, more raised beneath. Flowers not seen. Infructescence terminal (or from upper axils), solitary, 6–8.5 × 2.5–3.5 cm, capitate; peduncle 45–62 × 1.2–2.5 mm, reflexed at the base, compressed or subcylindrical, black, shaggy; bracts filiform, 4–12 × 0.1–0.8 mm, gathered in an apical mass beneath the fruits, subappressedly- or crispate-hairy. Drupes ellipsoid–obovoid, (9–)12–14 × 5–8 mm (exclusive of calyx), sessile, congested, 3–9 together in a spherical head to 3.5 cm diameter, hidden by bracts at the base, crowned by the calyx residue; exocarp jet black to reddish brown, usually set with pale raphides; fruiting sepals 5–6, free, linear, 6–7 × 0.8– 1 mm, ascending or curled, sparsely pilosulous; pyrenes 2, hemispherical; endocarp crustaceous, obtusely ridged on the back, commissural face slightly concave; preformed germination slits 2, marginal, extending halfway to the apex; seed without ethanol soluble pigments; endosperm ruminate.

Etymology: — Psychotria apdavisiana is named after A.P. Davis (Royal Botanic Gardens, Kew), a prominent contributor to our present understanding of the Psychotrieae.

Field characters: —Understory subshrubs perched on limestone boulders, 40–60 cm tall, erect; leafblades fleshy, bifacially dull green; peduncles reflexed; fruits globular or obovoid, 14–20 mm diameter in vivo, sessile, asymmetric, spongious, dull white, exocarp often dimpled.

Distribution: —Endemic to uninhabited uplands in the Strickland drainage of Western Province ( Fig. 4 A ).

Habitat and ecology: —Epilithic on limestone in perhumid montane forest, 910 m.

Phenology: —Fruiting in February.

Notes: —The new species is a miniature monocaul with tightly reflexed peduncles. Among Papuasian congeners, only Psychotria reflexapedunculata Sohmer (1988: 252) has this bizarre combination of features, but the capitate infructescence of P. apdavisiana is instantly distinguishing.

The unusually filiform calyces of the new Psychotria also recall P. phaeochlamys ( Lauterbach & Schumann 1901: 581) Valeton (1927: 95) , a congener with a similar headlike inflorescence but lacking a peduncle, and with red-colored drupes (not white). Any similarity with this latter species is probably superficial ( Fig. 5 ).

Although one plant was seen with an axillary peduncle (apparently resulting from apical growth after flowering; Fig. 1 A ) the new species is undoubtedly a Psychotria as defined by current interpretation of the Psychotrieae (in Davis & Bridson 2001, 2004, Davis et al. 2001, Sohmer & Davis 2007, Barrabé et al. 2012). Diagnostic support for the generic assignment is indicated by the paired pyrenes with marginal germination slits (2) on endocarps.

Numerous novelties are being revealed by recent surveys of PNG's interior karst environments—many with exceptional qualities enabling immediate determination as nova. The continuing discoveries are a convincing corroboration of conservation estimates regarding limestone environments in the southern ranges (e.g., Beehler 1993, Sekhran & Miller 1994).

Figures

FIGURE 1. Psychotria apdavisiana W.N.Takeuchi. A, the new plant has an untidy appearance, with stems and leaf surfaces often obscured by soil, epiphytic liverworts, and humified litter (plant shown was uprooted from its dark understory habitat and moved into sunlight); B, closer view of the irregularly shaped fruits. A–B from Takeuchi, Gambia & Jisaka 23261.

FIGURE 2. Psychotria apdavisiana W.N.Takeuchi. A, stipule (from Takeuchi, Gambia & Jisaka 23261).

FIGURE 3. Psychotria apdavisiana W.N.Takeuchi. A, fruiting habit, peduncles reflexed; B, as for 'A', appearance after drying. A–B from Takeuchi, Gambia & Jisaka 23261.

FIGURE 4. Island of New Guinea. A, Juha South, type locality for Psychotria apdavisiana. Overlay (shaded area) shows distribution of the southern karst formations.

FIGURE 5. Psychotria phaeochlamys (Lauterb. & K.Schum.) Valeton. A, immature head with subtending mass of linear bracts; B, anthetic flowers; C, ripening fruits; D, flowering aspect. Photos without collection, Strickland drainage.