Psychotria dieniensis Merr. & Perry var. banakii 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 : 23-24

Psychotria dieniensis Merr. & Perry var. banakii Takeuchi , var. nov. ( Fig. 3 )

A varietate typica arboribus 4–5 m altis (nec fructibus 0.5–2 m); laminis chartaceis subglabris (nec coriaceis pilosis) majoribus (10–)15.5–26 × (3.5–) 6–10.5 cm plerumque obovato-oblanceolatis (nec ellipticis) nervis lateralibus utrinsecus 12–17 (nec 8–11); inflorescentiis majoribus usque ad 96 × 45 mm; corollis tubis extus glabris (nec pilosis); fructibus ellipsoideis (nec globosis) usque ad 9 × 5.5 mm differt.

Type: — PAPUA NEW GUINEA. Western Province: Strickland drainage, Muller Range, Gugusu (Expedition Camp 1), lowland hill forest, 5°43.575'S, 142°15.630'E, 535 m, 9 September 2009, Takeuchi, Ama & Gamui 24549 (holotype: LAE; isotypes: A, BO, CANB, K, L, MO) .

Etymology: —Named after Banak Gamui of the PNG Institute of Biological Research.

Field characters: —Trees 4–5 m tall; branchlets fleshy, smooth, green; stipules foliaceous, notched or cleft, light green; leaf-blades rugose, dark green above, pale green beneath; panicle axes light green, canescent; flowers sessile; calyx lobes elongate, linear-deltate; corolla obtuse in bud, lobes 5, white, recurved at anthesis, throat white-hairy; stamens 5, exserted, white; style included, much shorter than the filaments; stigma 2-fid; fruit (immature) ellipsoid, whitish green.

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

Habitat and ecology: —Lowland hill forest, natural-growth communities at 535 m.

Phenology: —Flowering and fruiting in September.

Additional specimen examined: — PAPUA NEW GUINEA. Western Province: Muller Range, Gugusu (Expedition Camp 1), lowland hill forest, 5°43.635'S, 142°15.733'E, 535 m, 6 September 2009, Takeuchi, Ama & Gamui 24471 ( A, BO, CANB, K, L, LAE, MO) .

The new variety is clearly connected to P. dieniensis ( Merrill & Perry 1946) . Except for the distinctions specified by diagnosis, the vegetative and reproductive characteristics of var. banakii agree reasonably well with those in var. dieniensis . The differences argue for recognition only at infraspecific level. In comparison with P. leptothyrsa var. defretesiana ( Takeuchi 2009b) , the newly established variety is unlikely to require future consideration as a separate species.

Psychotria dieniensis sens. str. is represented mainly by subshrubs with commensurately small structures. Although the type (for P. dieniensis ) was taken from a lowland environment (500 m; Merrill & Perry 1946), an overwhelming majority of conspecific collections are from montane habitats straddling the Central Divide. The high-elevation populations have attributes typical of such areas (e.g., firm-textured leaf-blades, dense indument, contracted internodes, and low-bushy architectures). Unlike these earlier gatherings, the Muller Range collections are arborescent plants with correspondingly larger parts. The glabrate leaves of var. banakii for example, are substantially above the previous measurement range for P. dieniensis (reported as 4.5–14.5 × 1.5–4.5 cm in Sohmer 1988: 82). The var. nov. also has panicles and fruits suggestive of changes in structural form (viz., towards verticillate branching in the inflorescence and fruits decidedly longer than broad).

The robust features of var. banakii cannot be explained entirely by differences in elevation, given that the type for P. dieniensis was also taken from a lowland habitat. Despite its presumed status as a discrete variant from limestone, the perception of varietal distinction is complicated by geographic gaps in existing documentation, particularly from colline environments below 1000 m. The possibility of morphological discontinuities being removed by future collections cannot be discounted. Although additional sampling from the Southern Escarpment would be undoubtedly rewarding, the logistical and financial obstacles are severely limiting. In light of the operational and budgetary difficulties experienced by recent surveys on the karst, it is very unlikely that such localities can be revisited anytime soon.

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 3. Psychotria dieniensis var. banakii. Developmental stages of the inflorescence. A, immature inflorescence prior to peduncle elongation, partly enclosed by apically bifid stipules; B, anthesis, 4(–5)-merous flowers disposed in capitate clusters; C, post-anthesis, 3–4-verticillate branching of the lateral axes (mostly opposite branching in var. dieniensis). The linear, primary bracts are fragile and easily lost in the press, with only the bract bases or their abscission scars remaining on exsiccatae. The white indument on living plants invariably turns reddish-brown after drying. A–C from Takeuchi et al. 24549.