Raveniopsis microphyllus K.Wurdack, 2017

Wurdack, Kenneth J., 2017, A new tiny-leaved species of Raveniopsis (Rutaceae) from the Pakaraima Mountains of Guyana, PhytoKeys 91, pp. 1-12 : 3-5

Raveniopsis microphyllus K.Wurdack sp. nov. Figure 1

Diagnosis.

Differs from Raveniopsis breweri in small trifoliate leaves, indument of small rosulate trichomes, subsessile and few-flowered inflorescences, smaller sepals and corollas, and hirsute anthers.

Type.

GUYANA. Cuyuni-Mazaruni Region: Summit of Kamakusa Mtn. (i.e., on top of 4th escarpment of four), impenetrable elfin forest to 3 m, extremely dense and wet, rich in epiphytes, 5°52'51.7"N, 60°6'10.4"W, 1686 m, 7 Jun 2012 (fl), E. Tripp 3191 with K. Wurdack, A. Radosavljevic, and J. Ralph (holotype: BRG; isotypes: NY, US-3679224) .

Description.

Shrub to 1.5 m, evergreen; leafy ultimate branchlets thin, 0.7-0.9 mm dia., densely pubescent; trichomes rosulate, 0.2 mm wide, sessile to shortly stipitate, with numerous short, uniform-length radii (arms), radii free without coherent edges; bark dark-brown, thin, easily peeled; bark of older twigs with fissures from periderm development, pubescence persistent on strips of remaining epidermis. Stipules absent. Leaves opposite, 3-foliolate, petiolate; petiole terete, 2.5-3 × 0.7 mm; leaflets elliptic, subequal, laminar size class leptophyll, margin entire, unlobed; terminal leaflet with petiolule 1-1.5 mm long, lamina 5.5-7.5 × 3-5.3 mm, length:width ratio 1.32-1.83 (mean=1.63, n=11), base cuneate, symmetric, apex angle acute, apex shape sub-acute to obtuse; lateral leaflets usually slightly larger than terminal, petiolules 0.3-0.5 mm long, lamina 5-8.8 × 3-4.5 mm, length:width ratio 1.67-1.97 (mean = 1.84, n = 11; measurements of lateral leaflets from same leaves used in prior terminal leaflet ratio), base subcordate, basal extension asymmetrical, proximal basal extension (outer lobe) 0.3 mm, distal basal extension (inner lobe) 0.1 mm, apex similar to terminal leaflet; adaxial side dark green in life, moderately pubescent, becoming glabrescent with age; adaxial trichomes multiradiate, radii 10-13, free, lateral radii 0.1-0.2 mm long, central radius sometimes differentiated by elongation to 0.6 mm and porrect (porrect-multiradiate), trichomes near leaf base and margins having the greatest central radius elongation; abaxial side densely pubescent with rosulate trichomes; blade coriaceous, pellucid dots not visible, cross-sectional profile 0.7 mm high including 0.4 mm lamina thickness plus 0.3 mm layer of abaxial trichomes, primary venation pinnate. Inflorescence terminal, subsessile, flowers 1(-3) in a reduced monochasium. Flowers bisexual, 5-merous, shortly pedicellate, pedicel to 1 mm long. Calyx 5-parted, sepals connate at base to 1mm, separate distally, coriaceous; sepal lobes erect, unequal, in 2 alternating size classes; longer 2, 2-3 × 1 mm, unequal with longest subtending banner petal lobe; shorter 3, 1-2 × 0.5 mm, subequal; externally pubescent with trichomes of both porrect-multiradiate and multiradiate types, internally glabrous and lined with files of dark-content cells. Corolla white, tubular-infundabuliform, of 5 connate petals, markedly zygomorphic, 12-15 mm long; tube 8-9 mm long, slightly curved, narrowest point at base 0.9-1.2 mm dia., distally expanded to 1.5-2 mm dia.; lobes 5, imbricate in bud, spreading at anthesis with 4 in 1 plane forming slightly recurved lip and 1 upright banner, 2-3.5 × 1.5-2 mm, subequal, internal pilose band below lobes (zone where androecium is similarly pilose), glabrous elsewhere internally and externally where imbricate petal margins overlap in bud, externally tube otherwise densely multiradiate pubescent becoming porrect-multiradiate towards lobes. Androecium of 2 fertile stamens and 3 staminodes, free from corolla. Fertile-stamens proximally fused, distally separate but coherent with tangled trichomes, 11.5-12 mm long; filaments 9-10 mm long × ca 0.4 mm wide (per filament) at base, expanding to 0.8 mm wide distally due to asymmetric wings (wider on outer edge, narrower on coherent edge), narrowly oblanceolate, flattened, <0.1 mm thick, central vein prominent; apex of filament abruptly narrowed as 0.3 × 0.1 mm extension connected to anther; fused base and apical extension glabrous, free part pubescent with long crinkled (pilose) trichomes; anthers 2-2.2 mm long, consisting of 1.3-1.5 × 0.9 × 0.5 (thick) mm thecae, 0.5 mm basal saccate appendage, and 0.1 mm acute connective tip, basifixed, free (not laterally coherent along adjacent edges); thecae co-lateral with longitudinal dehiscence slits facing inner side of stamen, hirsute with stiff simple trichomes; basal appendage facing inner (dehiscence) side of stamen, glabrous; connective, tip, and basal appendage darkened and appearing glandular. Staminodes 3, free, 11-11.5 mm long; filament portion 9-9.5 mm, flattened and resembling slightly reduced fertile anthers, 0.2 mm wide at base to 0.5 mm distally, distal part pilose; apical tip extension 1.8-2 × 0.2 mm, subulate, undifferentiated with no trace of abortive thecae or distinction between filament apex and connective, glabrous to sparsely hirsute. Ovary 0.5 mm (high) × ca 1 mm (wide), 5-lobed (apocarpous), glabrous, surrounded by a thin cupular disc; disc erect, distinctly shorter than ovary, 0.3 mm high, slightly lobed at apex. Style single, 6 × 0.1 mm, glabrous; stigma ca 0.3 mm long, obliquely 5-lobed, smooth. Fruit not seen.

Etymology.

The specific epithet is derived from micro - (Greek, little or small) and - phyllus (Greek, -leaved), and refers to the small leaflet size, which is more reduced than in any other species of Raveniopsis .

Distribution and ecology.

Raveniopsis microphyllus is known only from the summit of Kamakusa Mtn. where it was occasional along a transect cut across the north-south axis of the narrow summit (personal observation). Flowers and young buds, although infrequent, were collected in June. The cold, wet, windswept summit of Kamakusa Mtn. is covered by a relatively low-stature (2-4 m tall) evergreen shrubland on peat overlying sandstone and can be classified in the upper montane life zone ( Huber 1995b). The flora contains dense stands of Bonnetia tepuiensis Kobuski & Steyerm. and B. roraimae Oliv. ( Bonnetiaceae ), along with other montane elements such and Schefflera monosperma Maguire, Steyerm. & Frodin ( Araliaceae ), species of Weinmannia L. ( Cunoniaceae ), and at least one other undescribed endemic plant ( Tryssophyton Wurdack, Melastomatacaeae). Immediately south of Kamakusa Mtn. along the wet edge of the Pakaraima Mtns. continues an unexplored and poorly mapped montane ridgeline with peaks. This local region includes some other>1500 m elevations, that while lower than the Kamakusa Mtn. summit (1686 m) are still within the 1500-3000 m highlands physiography ( Huber 1995a). However, these nearby peaks appear less likely to contain additional populations of R. microphyllus due to their small sizes, and lower elevations that tend to support slightly different and taller plant communities. The closest peak (55 km SSE) to reach or exceed the elevation of Kamakusa Mtn. is relatively well-explored Mt. Ayanganna (2041 m), which has so far only yielded Raveniopsis ruellioides (Oliv.) R.S. Cowan.

Conservation status.

Following the criteria and categories of IUCN (2012), Raveniopsis microphyllus is given a preliminary status of Vulnerable (VU D2) due to population very small or restricted (area of occupancy <20km2 and number of locations <5). The species has extremely limited suitable montane habitat and coupled with relatively small known population size is vulnerable to climate and land use changes.

The upper part of Kamakusa Mtn. is presently pristine and undisturbed habitat, and the sole known Raveniopsis microphyllus population had no evidence of being unhealthy or fluctuating. The region is at risk of habitat destruction due to placer gold mining, although such activity is unlikely to reach the small, inhospitable summit of Kamakusa Mtn. Recent gold mining of moderate scale has occurred along the upper Partang River on the southern edge of Kamakusa Mtn. and its drainage, about 10 km from the type locality. While those mining operations had ceased by 2012, other waves of gold prospecting activities go back decades and have pushed further in. Such activities were noted as "pork-knocker camps" on Tillett et al. herbarium labels of 1960 (e.g., Aechmea pallida L.B. Sm. [ Bromeliaceae ], Tillett 44859, NY), and during the recent fieldwork (personal observation) that encountered old camps (furthest human intrusion was a long overgrown camp at N05°51'44.4", W060°09'20.5", 1019 m, and 6.2 km from the type locality), an abandoned unpaved runway (Partang airstrip), and ATV trails from the nearest village (Imbaimadai), which were constructed to support the recent upper Partang River mining operation.

Figures

Figure 1. Illustration of Raveniopsis microphyllus. A Habit B Flowering branch C Trifoliate leaf D Flower (face view) E Flower (lateral view) F Calyx with five unequal sepals G Gynoecium H Corolla (split) and androecium I Androecium of bud J Floral dissection of same bud. (Source: Tripp 3191, US).