Pteris tahuataensis Lorence & K. R. Wood, 2011

Lorence, David H., Wagner, Warren L., Wood, Kenneth R. & Smith, Alan R., 2011, New pteridophyte species and combinations from the Marquesas Islands, French Polynesia, PhytoKeys 4, pp. 5-51 : 20-21

8. Pteris tahuataensis Lorence & K. R. Wood sp. nov. Figs 10 15E

Latin.

Ab aliis Marquesas speciebus laminis 1-pinnatis usque ad 1-pinnato-pinnatifidis, distalibus pinnis non alatis, et glabris ver glabrescentibus stipitibus differt.

Type.

Marquesas Islands: Tahuata: Hanatetena, main valley, first deep gulch to the north, general UTM 0710938 - 8899189, 518 m, 2 Feb 2003,K. R. Wood 10083 (Holotype: PTBG-04297!; Isotypes P!, PAP!, UC!, US!).

Description.

Terrestrial or lithophytic ferns; rhizomes creeping to suberect, 2-5 cm long, 1-3 cm in diameter, clothed in fine, golden-brown acicular hairs 1-2.5 mm long; fronds 15-20 per rhizome, pendent, 35-125 cm long; stipes ca. ½ length of frond, up to 4 mm in diameter, atrocastaneous to stramineous, grooved adaxially, sparsely pustulate, glabrous except for a sparse cover of linear to linear-lanceoate, tan-brown scales 3-5 × 0.3-0.5 mm at base of stipes; blades chartaceous, glabrous, ovate, 18-65 × 12-35 cm, ovate. with 5-7 pairs of pinnae; proximal 1-3 pinnaepairs 1 –(2–) pinnate-pinnatifid, up to 34 cm long, sessile or stalked up to 9 mm, base obtuse to truncate, uniauriculate or bearing 2-3 pair of falcate lobes or with proximal pair occasionally dividing into falcate pinnules 5-13 cm × 1.4-1.7 mm, reaching maximum length basiscopically on lowest pinnae, apices acute to cuneate, or attenuate, margins crenate to dentate; distal part of blade composed of 3-5 pinnae pairs, these simple, falcate, subopposite, up to 23 cm long, the bases sessile, obtuse to truncate, sometimes uniauriculate acroscopically, tapering gradually to cuneate or attenuate apices with crenate-dentate margins, the single terminal pinna free or sometimes adnate basally to the distal pinnae pair, 6.5-23 × 1.0-2.5 cm, apex attenuate, crenate; costaeand costules grooved adaxially, rounded abaxially, similar to stipe in color; veins netted with 2-3 rows of areoles. Sori with indusia 0.5-0.9 mm wide, olivaceous; sori usually absent at apices of pinnae, Spores castaneous.

Distribution.

Known only from Tahuata, Marquesas Islands.

Ecology.

This new terrestrial or lithophytic species occurs in wet forests and shrublands from about 418 to 914 m elevation, usually on windswept vertical cliffs in water seepage. A population of approximately 50-70 plants was observed at 914 m on windswept vertical cliffs around a natural spring on saturated basalt walls with Leptochloa marquisensis (F. Br.) P. M. Peterson & Judz. and Selliguea feeioides Copel., mosses, and lichens in wet forest of Crossostylis biflora , Freycinetia sp., Metrosideros collina , Reynoldsia marchionensis , Weinmannia marquesana var. marquesana, Myrsine grantii , and Pandanus tectorius . A second population occurs at 518 m in mesic forest with Cerbera manghas L., Cyclophyllum barbatum , Hibiscus tiliaceus , Pandanus tectorius , Sapindus saponaria L. and Xylosma suaveolens subsp. pubigerum. A third population is from lowland degraded mesic forest at 418 m elevation with Cerbera manghas , Cyclophyllum barbatum , Ficus prolixa var. prolixa, Hibiscus tiliaceus , Pandanus tectorius , and Xylosma suaveolens subsp. pubigerum, Sapindus saponaria. The main threats to this species include competition from invasive alien plant species and habitat destruction by feral goats and fire at lower elevations. Known only from three collections, the one population at 418 m having an estimated 50-70 plants (Wood 10085), the others were isolated plants.

Conservation status.

Proposed IUCN Red List Category Critically Endangered (CR): B2a, B2b i–iii; D): B2: total area of occupancy less than 10 km2 (ca. 5 km2); B2a, three populations known; b ( i–iii), habitat continuing decline inferred; D, population estimated to number fewer than 250 mature individuals. The suitable habitat for Pteris tahuataensis on Tahuata (ca. 61 km2) is indicated as an endangered environment, threatened by human activity (deforestation, fire), feral animals, and invasive plants, reducing the extent of the forest. D, the rarity of this species is supported by the lack of collections and the small extant area, i.e. with only three known collections and an estimated total population size of fewer than 250 plants.

Etymology.

This new species is named for its only known island of occurrence.

Specimens examined.

Marquesas Islands: Tahuata: Hapatoni, village to the south of Vaitahu, ridge to summit above Patikoea point, UTM 0706136-8897872, 418 m, Wood 10085 (BISH, K, MO, NY, P, PAP, PTBG, UC, US); Amatea region, locations around Haaoiputeomo satellite dish, 9°92'S, 139°8'W, 914 m, Wood 10250 (PTBG, US).

Figures

Figure 10. Pteris tahuataensis Lorence & K. R. Wood. A habit B blade C fertile pinna distal part D lower surface of fertile pinnule showing marginal sori E rhizome scale. Drawn from the type collection (Wood 10083) and field images.

Figure 15. A Polystichum uahukaense, frond (Ua Huka, Wood 10518) B Pteris hivaoaensis (Hiva Oa, Wood 4374) C, D Pteris marquesensis C frond D rhizome and stipe bases (both Hiva Oa, Wood 10871) E Pteris tahuataensis (Tahuata, Wood 10083) F Thelypteris marquesensis, habit, colony on wet rock face (Hiva Oa, Wood 4408).