Psychotria stolonifera Takeuchi, 2010

Takeuchi, Wayne, 2010, Additions to the rubiaceous flora of Papua New Guinea: Psychotria stolonifera and P. ternatifolia, two remarkable species from the Muller limestone, Phytotaxa 7, pp. 25-34 : 25-29

Psychotria stolonifera Takeuchi , sp. nov. ( Figs. 1–4 )

Inter species congeneris Papuasiae caulibus partim basalibus stoloniformis partim erectis vel ascendentibus 0.1–0.4(– 1.0) m altis statim distinguitur.

Type: — PAPUA NEW GUINEA. Western Province: Muller Range, Expedition Camp 2, Nothofagus - emergent montane forest on doline karst, 5°39.652'S, 142°17.962'E, 1425 m, 16 September 2009, Takeuchi, Ama & Gamui 24691 (holotype LAE; isotypes A, BO, K, L) .

Subshrubs 0.1–0.4(–1.0) m tall. Basal stems runner-like, internodes adventitiously rooting or not. Ascending stems unbranched (or sparingly branched), terete, 1–3 mm diameter, ± compressed near apices, glabrous, without lenticels; surfaces nigrescent, smooth or obscurely wrinkled; internodes (0.5–)2.0–6.0(–8.5) cm, often with raised decussate lines. Leaves cauline, 4–7 pairs and/or with 2–4(–6) pairs on short branches, equal, glabrous; stipules subpersisting, disclosing a nodal ring of appressed hairs after falling, free, ovate, 9– 19 × 4–8 mm, notched 2–6(–9) mm from the top, dull black, densely tomentose-lanate on the inner side, glabrous on the outside; petioles 5–15 × 0.4–0.9 mm, planoconvex; leaf-blades chartaceous-subcoriaceous, elliptic (or lanceolate), (2.8–)4.5–8.0(–9.5) × (0.9–) 1.6–3.3 cm; base cuneate-subattenuate; margin entire, inconspicuously furnished with antrorse hairs; apex acuminate; lamina surfaces fuliginous (or rufescent), cystoliths linear, infrequent; domatia absent; venation camptodromous, secondary veins 7–12(–16) per side, 2–6(–10) mm apart, arcuate, filiform, at the lamina center with divergence angles of 50–75°; reticulum irregular, coarsely areolate, obscure or invisible; midribs prominulous on both sides; higher order nerves weakly raised or planate above, more raised beneath. Inflorescence terminal, paniculiform, dichasial, 15–37 × 10–20 mm, erect, papillate-puberulent, glabrescent; axes black, terete or compressed; peduncle 3–10(–21) × 0.5–1.0 mm, (6–)15–28 × 0.5–1.2 mm in fruit; axis ca. 10 × 0.8 mm, to ca. 13 × 1.1 mm in fruit; branches opposed, contracted, crowded; primary (axis) bracts hair-like, (3.5–)7.5–12.0 × 0.3–1.0 mm, diverging, crispate; higher order bracts 3–5 × 0.1–0.2 mm. Flowers (measurements from spirit-preserved material) heterostylous, dimorphic, pentamerous; pedicels 0.5–3.0 mm long, not articulate. Short-styled flower: hypanthium synsepalous, infundibular, calyx tube (with ovary) 2.0 × 1.8–2.0 mm, calyx lobes 3 × 0.7–1.0 mm; corolla valvate in bud, obtuse, fleshy, exterior surfaces glabrous at anthesis, inside with a 2 mm wide hair-ring starting at the throat, corolla tube cylindrical, 5 × 1.5–2.0 mm, corolla lobes elliptic, 4.0–4.5 × 1.5– 2.0 mm, reflexed; stamens antesepalous, glabrous, erect, inserted within the hair-ring, filaments ca. 2 × 0.2 mm, anthers exserted, oblongoid, 1.5 × 0.5–0.7 mm, basifixed, introrse; ovary bilocular, ovule erect, one per cell; disk globuliform, fleshy, glabrous, recessed at the summit; style cylindrical, ca. 3 × 0.2 mm, stigma included, ca. 1.5 × 0.5 mm, bilobed, papillate. Long-styled flower as for the short-styled form but with the following differences: hypanthium subglobose, ± compressed, calyx tube (with ovary) 2.5 × 1.5–2.8 mm, calyx lobes triangular, ca. 1 × 1 mm; corolla tube 4–5 × 2–3 mm, wider at the base, corolla lobes ovate, 4–5 × 3.0– 3.5 mm, costate, hair-ring ca. 0.3 mm wide, positioned at the throat and not extending to the staminal insertion; stamens included, filaments ca. 0.5 × 0.2 mm, anthers 1.3–1.4 × 0.6 mm; style ca. 5 × 0.2 mm, stigma exserted, capitate, ca. 0.8 × 1.5 mm. Fruits arranged in congested cymules, ellipsoid-obovoid, 5.5–8.0 × 3.5–5.5 mm, compressed or not; pedicels cylindrical, (0.8–)1.2–3.0 × 0.3–0.5 mm; exocarp black, usually set with pale raphides; calyx lobes persisting to fruit maturity, ligulate, 2.7–4.0 × 0.2–0.5(–1.0) mm, ascending; pyrenes 2, hemispherical; endocarp crustaceous, ± corrugate but not dorsally ridged, weakly furrowed on the commissural face; preformed germination slits 2, marginal, extending 1/4–1/3 the pyrene length; endosperm conspicuously ruminate.

Field characters: —Subshrubs growing in congested thickets, never as solitary plants; basal stems plagiotropic, tenaciously rooted; ascending stems green, smooth, fragile; stipules hyaline; leaf-blades fleshy or herbaceous, bifacially green, rugose, undulate; corolla white; stamens white; drupes spongious, white; pyrene black.

Distribution: —Known thus far only from the type locality ( Fig. 5 ).

Habitat and ecology: — Nothofagus -emergent montane forest on doline karst, 1425–1495 m.

Phenology: —Flowering and fruiting in September.

Additional specimens examined: — PAPUA NEW GUINEA. Western Province: Muller Range, Expedition Camp 2, Nothofagus -emergent montane forest on doline karst, 5°39.530'S, 142°18.105'E, 1495 m, 13 September 2009, Takeuchi, Ama & Gamui 24618 A ( A, LAE) ; 5°39.638'S, 142°18.018'E, 1460 m, 15 September 2009, Takeuchi , Ama & Gamui 24683 ( A, K, L, LAE); 5°39.610'S, 142°18.018'E, 1450 m, 17 September 2009, Takeuchi, Ama & Gamui 24707 ( A, BISH, K, LAE) .

The new species is known only as radially-spreading plants on doline limestone. Its diminutive stems (mostly <50 cm, rarely to 1.0 m tall), are sequentially produced from near-surface stolons. Although Psychotria leptothyrsa var. defretesiana ( Takeuchi 2009: 176) was recently characterized as being the smallest Psychotria in Papuasia, P. stolonifera is often of similar stature. Many plants are fruit-bearing when only 15–20 cm tall.

The presence of a corolline hair-ring and the insertion of stamens within that ring, are (inter alia) defining generic traits for Psychotria (Davis & Bridson 2001, 2004, Davis et al. 2001). Short-styled flowers of P. stolonifera show these features clearly, but in the long-styled form the hair-band is considerably contracted (0.3 mm versus 2.0 mm wide), with the stamens distinctly positioned below the hairs. Except for this dimorphism, the new species conforms in detail to the generic circumscriptions established by modern study of the Psychotrieae (e.g., in Davis & Bridson 2001, 2004, Davis et al. 2001, Sohmer 1988, Sohmer & Davis 2007). Irrespective of the hair-band discrepancies, the preformed germination slits (2) on pyrene margins are indicative of Psychotria ( Sohmer & Davis 2007) and provide diagnostic support for the generic assignment.

Figures

FIGURE 1. Psychotria stolonifera. A, forming a dense groundcover on limestone karst, stems 15–20 cm tall (Takeuchi et al. 24618A); B, blue scale bar with white lines marked in 1 cm increments.

FIGURE 2. Psychotria stolonifera. A, uprooted plants, showing runner-like shoots with adventitious roots and erect stalks (Takeuchi et al. 24707).

FIGURE 3. Psychotria stolonifera. A, vegetative stems; B, stipules. A–B from Takeuchi et al. 24707.

FIGURE 4. Psychotria stolonifera. A, long-styled flowers with stigma exserted; B, short-styled flowers with anthers exserted; C, developing (immature) fruits; D, ripe drupes; E, pyrene (6 × 4 mm), adaxial surface with preformed germination slits on margins. A from Takeuchi et al. 24691; B–C from Takeuchi et al. 24683; D–E from Takeuchi et al. 24618A.

FIGURE 5. Island of New Guinea. A, Muller Range, Bivouac 2, type locality for Psychotria stolonifera and P. ternatifolia. Shaded circle for visual emphasis only (not indicative of observed or potential distribution).