Rhysotoechia welzeniana W.N.Takeuchi, 2012

Takeuchi, Wayne, 2012, Modern sequels to the Kaiserin-Augusta-Fluss itinerary of Carl Ledermann: Rhysotoechia welzeniana sp. nov. (Sapindaceae), a remarkable species from the upper Sepik of Papua New Guinea, Phytotaxa 61, pp. 55-60 : 56-60

Rhysotoechia welzeniana W.N.Takeuchi , sp. nov. ( Figs. 1–3 )

Inter speciebus Rhysotoechiae singularis plantis dioicis foliis simplicibus haud pinnatis statim distinguitur. Type: — PAPUA NEW GUINEA. East Sepik Province: April River, lower slopes of Kamelsrücken, opposite Natawe , margin of seasonally flooded swamp forest, 4°35'S, 142°33'E, 100 m, 14 November 2011, Takeuchi, Gambia & Ama 26239 (holotype A!; isotypes BO!, CANB!, K!, L!, LAE! [2 sheets]) .

Shrubs, 1.5–4 m tall, dioecious. Stems terete, 6–14 mm diameter near the top, appressed-puberulent, glabrescent, longitudinally lined, dark brown to fuliginous, lenticellate, lacking abscission scars, pithy. Leaves spirally inserted, isomorphic, simple, not unifoliolate, crowded, exstipulate, without hairs; petioles 5–15(–20) × 5–9 mm, planoconvex, not articulated, surfaces dull black, cerebriform-wrinkled; leaf-blades linearoblanceolate, (37–)41–78(–86) × (10–) 14–22 cm, coriaceous; bifacially bright green (sometimes marked by brownish patches), pusticulate, obscurely lepidote or granulate, domatia absent; lamina base gradually tapered to the petiole, equal; margins entire; apex obtuse, acute, or acuminate, acumen 0.8–1.5 × 0.5–1.5 cm when present; venation camptodromous (or craspedromous-reticulate); secondaries 20–29(–35) per side, at the lamina center straight-diverging (55–)65–85° from midrib, (1.2–)1.5–3.4(–4.1) cm apart, gradually or abruptly curved near the margin, partial intersecondary veins often interposed between the main laterals; tertiary venation reticulate, dense, conspicuous, tessellate, areoles mostly irregular; midrib adaxially prominent, abaxially keeled; all higher order nerves distinctly raised on both sides. Staminate inflorescences axillary, solitary or 2–3 together, a racemiform thyrse (3–)6.2–19.3 × (0.5–) 1–1.5 cm, ascending, puberulent on all axial surfaces; peduncle 8–30 × 1–1.5 mm, compressed, striate; lateral branches to ca. 8 mm long; bracts scalelike, ovate, 0.7–1.1 × 0.3–0.6 mm, falling after anthesis; bracteoles (pedicel bracts) similar but smaller, to 0.6 × 0.5 mm; pedicels 1.7–3 × 0.2–0.3 mm, not articulated. Staminate flowers (measurements from spirit-preserved material) globose in bud; perianth 5-merous, glabrous, free; sepals obtusely ovate or elliptic, concave, glandular-spotted, unequal, 2 outer sepals smallest, ca. 2 × 2.5 mm, 3 inner sepals 3.5–4 × 2– 3 mm, margins membranous; petals inserted in disk sinuses, flabellate, 2.9–3.2 × 1.9–2.2 mm inclusive of the (0.5–)0.8–1.3 × 0.4–0.8 mm claw, pilose, basal scales 2, adaxial, oblong, ca. 1 × 0.6 mm; disk complete, glabrous, scalloped, fleshy; stamens (7–)8, overall length 3.2–3.5 mm, connivent, erect; filaments densely pilose in the lower 2/3, glabrous in the upper 1/3; anthers basifixed, latrorse, exserted, furnished with short patent hairs, anther cells ellipsoid; pistillode globular-conoid, ca. 1 × 0.8 mm, included, hirtellous. Pistillate inflorescences 7.5–12 × 1–1.5 cm, solitary or up to 6 together, other characters as for the staminate inflorescences. Pistillate flowers (measurements from rehydrated material) like the staminate flower except for the following: fertile stamens none; staminodes (7–)8, overall length ca. 1.5 mm, otherwise with same appearance as the functional stamens; gynoecium 4.5–5 mm long, hirtellous; ovary conoid, ca. 2.5 × 2 mm, acutely 3-angled, locules 3, each with 1 ovule; style exserted; stigma capitate, 3-lobed, papillate. Infructescence (seen only in rotting condition) axis to 17 x 0.5 cm; pedicels accrescent, to 12 × 4 mm. Fruits obovoid, ca. 3.5 × 3 cm, trigonous.

Etymology: — Rhysotoechia welzeniana is named after P.C. van Welzen (Naturalis Biodiversity Centre, Leiden, Netherlands), a systematist in the Euphorbiaceae and Sapindaceae of Malesia and Thailand.

Field characters: —Understory shrubs, 1.5–4 m tall, pole monocauls (or sparingly branched); leaves crowded, axils congested with forest litter; petioles swollen, purple-black; leaf-blades papyraceous, dark green above, slightly lighter green beneath; inflorescences erect, flowers (both sexes) pale whitish-yellow all parts; fruits (seen only in rotting condition) black, 3-angled, seed characters undeterminable due to the state of decomposition.

Distribution: —Known with certainty from the April River of East Sepik Province ( Fig. 4 ). Sterile plants, possibly of this species, have also been seen along other tributaries connecting into the Sepik main channel (pers. obs.).

Habitat and ecology: —Lowland forest on margins of seasonally flooded swamp, 100 m.

Phenology: —Flowering and with rotten fruits in November.

Additional specimen examined (paratype): — PAPUA NEW GUINEA. East Sepik Province: April River, lower slopes of Kamelsrücken, opposite Natawe , margin of seasonally flooded swamp forest, 4°35'S, 142°33'E, 100 m, 14 November 2011, Takeuchi, Gambia & Ama 26240 ( A! [2 sheets], BO!, K!, L! [2 sheets], LAE! [2 sheets]) .

Rhysotoechia welzeniana is the only member of its genus with foliage comprised entirely of simple leaves. The recently described R. etmanii Takeuchi (2001: 569) can also have simple leaves, but in that species the foliage is dimorphic: paripinnate leaves are always present at the apical nodes, in addition to the simple leaves at lower nodes (pers. obs.). In gross appearance, the new plant recalls Barringtonia Forster & Forster (1775: 75 , pl. 38), although the resemblance is superficial (the latter genus has stipulate leaves with conspicuous cataphylls, and the leaf-blade venation is not densely reticulate).

The discovery of dioecy in Rhysotoechia welzeniana is an unexpected development in a genus formerly composed only of monoecious plants. The previously described species of Rhysotoechia have seemingly bisexual flowers (functionally unisexual) but in R. welzeniana the flowers are obviously dimorphic even to the naked eye. Despite its unique features, the flower morphology is undoubtedly that of Rhysotoechia —no other sapindaceous genus will fit the character profile.

Although R. welzeniana is assumed to be dioecious on the basis of existing evidence, the presence of dichogamy (with three flower types) cannot be discounted (Welzen, pers. comm.). If dichogamous flowers in Rhysotoechia are confirmed by additional collecting, the present description will require future modification. Etman (1994a: 50) had earlier argued against the use of infrageneric classification in groups as small as Rhysotoechia . Given its unusual qualities however, R. welzeniana may warrant future recognition at sectional level.

The new plant will require several changes to the Flora Malesiana generic keys. With Key 1 ( Adema 1994: 435–440, as modified in Takeuchi 2001: 572), lead 11c should be amended as follows:

11c. Leaves paripinnate and/or simple ........................................................... Rhysotoechia ( R. etmanii and R. welzeniana )

With generic Key 2 ( Welzen 1994: 440–450, as modified in Takeuchi 2001: 573), lead 6c should be amended as follows:

6c. Fruits not winged. Leaves simple ............................................................. Rhysotoechia ( R. etmanii and R. welzeniana )

Rhysotoechia welzeniana can be added to the species key in Etman (1994a: 53) by inclusion of a third line

(1c) to the first couplet:

1a. Leaves 2–5-jugate, sometimes 1-jugate…................................................................................to the existing couplet 2 1b. Leaves 1-jugate, rarely 2-jugate................................................................................................................. R. bifoliolata 1c. Leaves simple, never pinnately compound............................................................................................... R. welzeniana

Irrespective of the existing keys, Rhysotoechia etmanii is the only species which can be mistaken for R. welzeniana , and then only in the case of an incomplete collection (of R. etmanii ) in which the apical leaves have been omitted. The following couplet provides a concise summary of the distinction between the two species:

1a. Montane trees with many branches; leaves dimorphic, paripinnate and simple, blades (on simple leaves) broadly oblanceolate, 25–39 × 9.5–15.5 cm; fruits obovoid, 1.9–2.7 × 1.3–1.6 cm, Eastern Highlands Province ..... R. etmanii

1b. Lowland shrubs, monocaulous (or sparingly branched); leaves isomorphic, always simple, blades linearoblanceolate, (37–)41–78(–86) × (10–) 14–22 cm; fruits obovoid, ca. 3.5 × 3 cm, East Sepik Province. R. welzeniana

Figures

FIGURE 1. Rhysotoechia welzeniana W.N.Takeuchi. Habit, 4 m pole shrub (Takeuchi et al. 26240).

FIGURE 2. Rhysotoechia welzeniana W.N.Takeuchi. Apical view of crown (Takeuchi et al. 26240).

FIGURE 3. Rhysotoechia welzeniana W.N.Takeuchi. A, pistillate plant with anthetic inflorescence; B, infructescence (fruit rotting); C, pistillate flowers, style exserted; D, staminate flowers (after drying), stamens exserted. A–C from Takeuchi et al. 26240 (paratype), D from Takeuchi et al. 26239 (type).

FIGURE 4. Island of New Guinea. A, Natawe-Kamelsrücken, April River type locality for Rhysotoechia welzeniana W.N.Takeuchi.