Psychotria stevedarwiniana Takeuchi, 2011

Takeuchi, Wayne, 2011, Additional notes on Psychotria (Rubiaceae) from the southern karst of Papua New Guinea: P. defretesiana comb. et stat. nov., P. dieniensis var. banakii var. nov., and P. stevedarwiniana sp. nov., Phytotaxa 24, pp. 19-27 : 24-26

Psychotria stevedarwiniana Takeuchi , sp. nov. ( Figs. 4–5 )

Inter speciebus congeneribus Papuasiae stipulis connatis magnis usque ad 8.5 × 1.7 cm (in vivo) tubis cum 4 appendicibus apicalibus 4–8 × 0.3–3 mm statim distinguitur.

Type: — PAPUA NEW GUINEA. Western Province: Muller Range, Sawetau (Expedition Camp 2), Nothofagus -emergent montane forest on doline karst, 5°39.638'S, 142°18.018'E, 1460 m, 15 September 2009, Takeuchi, Ama & Gamui 24688 (holotype: LAE; isotypes: A, K, L) .

Understory subshrubs, 0.5–1 m tall, monoaxial or sparingly branched, erect. Stems compressed near the top, 1.5–3 mm diam., fuliginous, hollow or pithy, often furrowed, with or without adventitious roots; indument pilose, dense, reddish-brown (white in vivo), persisting, longest hairs ca. 1.5 mm long; older axes terete, transversely cicatricose, lenticels absent; internodes 2.5–9.5(–12) cm long. Leaves cauline or in 1–4 pairs on short branches, equal, obliquely diverging; stipules ovoid-conoid (or subfusiform), (9–)20–60 × (2–) 4–12 mm, connate, tubular, caducous, disclosing a nodal ring of appressed colleters after falling, surfaces black, glabrous inside, pilosulous outside, apically (2–)4-lobulate (lobules 4–8 × 0.3–3 mm); petioles 10–32 × 1–2.5 mm, planoconvex or subcylindrical, indument as on stems; leaf-blades subcoriaceous, ovate-elliptic (or obovate), (7–)9.2–15.6 × (2.8–)4–8(–9.9) cm, base mostly obtuse, margin revolute, apex acuminate (acumen to ca. 1.5 × 1 cm); lamina surfaces fuliginous to rufescent; adaxially rugose, bullate, barbate at the petiole insertion otherwise glabrous; abaxially pilose on veins, velutinous between veins; raphides not seen; domatia absent; venation brochidodrome or camptodrome-reticulate, secondaries (6–)8–14 per side, (2–)6–16(–21) mm apart, at the lamina center straight-diverging (40–)50–70° from midribs, ± parallel, closing by gradually looping nerves (or anastomosing to the margin); partial intersecondaries often present; crossing (tertiary) nerves subscalariform; all veins impressed on the upper side, prominent beneath; reticulum conspicuous, coarsely areolate, tessellate. Inflorescence not seen. Infructescence terminal (or subapical by shoot overtopping), paniculiform, 35–60 mm long, ascending, ebracteate; primary axes 2–5 together, 20–45 × 0.8– 1.5 mm, terete; surfaces nigrescent, densely pilose; cymes 1–6 per primary axis, loose; secondary axes verticillately inserted or not; pedicels cylindrical, 2–4.5(–6.5) × 0.5–0.8 mm, not articulated. Fruits (immature) obovoid, 6.5–10 × 5–7.5 mm (exclusive of calyx), often asymmetric, hairy on all parts; exocarp jet black, raphides not seen; calyx persisting, united in the lower 0.2–1(–1.5) mm, lobes 5, triangular, 1–2 × 1.2– 1.5 mm, erect or reflexed; pyrenes hemispherical, dorsally ± smooth; preformed germination slits 2, marginal, extending the full length of the pyrene or ending just below the apex; seed coat with ethanol soluble pigments; endosperm ruminate.

Etymology: —Named after Prof. Steven P. Darwin (Tulane University), an authority on Pacific floras and the author's former associate in Hawaiian botany. The alternative epithet " darwiniana " has been preempted (in Cheek et al. 2008).

Field characters: —Miniature subshrubs 0.5–1.0 m tall; indument of white hairs on nearly all parts; stems monocaulous or at most with 1–3 branch pairs; stipules to 85 × 17 mm, inflated or not, off-white to light green, (2–)4-lobulate at the top (lobules 7–10 mm long); leaves thickly fleshy-coriaceous, rugose, bullate; fruits obovoid, epicarp entire, green.

Distribution: —Known only from the type locality ( Fig. 2 ).

Habitat and ecology: — Nothofagus -emergent montane forest on doline karst, 1425–1495 m. Occurring as scattered colonies restricted to dark understories, often in spatial association with P. stolonifera and P. ternatifolia .

Phenology: —Fruiting in September. Populations sterile except for the expedition's two collections.

Additional specimen examined: — PAPUA NEW GUINEA. Western Province: Muller Range, Sawetau (Expedition Camp 2), Nothofagus -emergent montane forest on doline karst, 5°39.638'S, 142°18.018'E, 1460 m, 15 September 2009, Takeuchi, Ama & Gamui 24671- B ( A, BO, CANB, K, L, LAE, MO) .

Even in a genus noted for morphological variation, the tubular stipules of P. stevedarwiniana are remarkable for their size and structure. The elongate-conoid (or subfusiform) stipule attains dimensions up to 85 × 17 mm in vivo, and is surmounted by four foliaceous lobes at the apical orifice. The process of stipule maturation is characterized by such pronounced changes in size, texture, and color, that the immature and mature stages look like structures from different species ( Fig. 4 ).

Among the 19 Papuasian congeners with connate stipules, P. stevedarwiniana is further distinguished in having conspicuously rugose-bullate leaves and basally branching panicles (the latter both terminal and subapical). The distinctive vegetative features allow for instant recognition whenever sterile plants are encountered.

Although its flowers are still unknown, the pyrenes of P. stevedarwiniana are characteristic of Psychotria in the sense established by modern study of the Psychotrieae (sensu Davis & Bridson 2001, 2004, Davis et al. 2001, Sohmer & Davis 2007). Despite the novelty's atypical qualities, compelling support for the generic assignment is provided by the paired pyrenes with preformed germination slits (2) confined to the margins.

Figures

FIGURE 2. Island of New Guinea. Collection localities. A, Baitanisa (lower Mamberamo basin), type locality for Psychotria leptothyrsa var. defretesiana; B, Muller Range, type locality for P. dieniensis var. banakii and P. stevedarwiniana. Overlay (shaded area) shows distribution of the southern karst formations.

FIGURE 4. Psychotria stevedarwiniana. A, stem with mature stipule; B, inset, upper left, stipule with circular cutout revealing the immature leaves (green) inside the tube; C, inset, lower left, nodal colleters (brown) uncovered by stipule abscission. A–C from Takeuchi et al. 24688.

FIGURE 5. Psychotria stevedarwiniana. A, vegetative habit, plants (3 shown) to ca. 30 cm tall; B, immature fruiting panicle. A–B from Takeuchi et al. 24688.