Polystichum uahukaense Lorence & W. L. Wagner, 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 : 16-17

5. Polystichum uahukaense Lorence & W. L. Wagner sp. nov. Figs 7 14F, 15A

Latin.

A Polytsicho marquisensi E. D. Br. minoribus rhizomatibus 3-4 cm. longis × 1.5-3 cm diametro, frondibus minoribus bipinnatibus cum laminis 26-58 × 12-27 cm, soris indusiatis differt.

Type.

Marquesas Islands: Ua Huka: Hane/Hokatu cliff zone, 520 m, 11 December 2003, K. R. Wood & J.-Y. Meyer 10518 (Holotype PTBG-042930!; Isotypes AD!, BISH!, K!, MO!, NY!, P!, PAP!, UC!, US!).

Description.

Terrestrial ferns; rhizomes short, erect or suberect, 3-4 cm long, 1.5-3 cm in diameter; rhizome scales 20-28 × 2-2.5 mm, linear-oblong, concolorous, medium to dark brown, margins entire or with occasional short teeth, cells linear, in sinuous files. Fronds 5-7 per rhizome; stipes 16-43 cm long, ½ -2/3 length of the blades, adaxially grooved, base with dense, linear to linear-oblong scales 10-20 × 1-2 mm, brown and similar to rhizome scales but with thinner, lacerate-dentate margins, mixed with smaller hairlike scales with lacerate bases, mid- to upper part of stipe with hairlike scales or glabrescent; blades ovate-oblong to narrowly oblong, 26-58 × 12-27 cm, bipinnate; rachises densely scaly with pale brown, hairlike scales 3-6 mm long with expanded lacerate base; pinnae 20-30 on a side, narrowly oblong, apex narrowly acute, largest pinnae 6-15 × 1.5-3 cm, lowermost 1(-2) pairs slightly reduced, costules adaxially grooved, pinnules 8-16 pairs per pinna, each incised acroscopically with a small auricle or basal pinnules of larger pinnae sometimes deeply incised forming a nearly free obovate lobe, pinnule apices acute to obtuse, both margins crenate, apex and lobes spinulose at tip; blades chartaceous to subcoriaceous, adaxially sparsely capitate-glandular when young, glabrate, abaxially with pale tan hairlike scales on costae, veins, and margins, veins forking, scarcely visible adaxially, slightly prominulous abaxially. Sori each with a peltate indusium 0.5-0.6 mm in diameter, tan, with numerous marginal projections, thin and often fugacious, not confluent at maturity. Spores black.

Distribution.

Marquesas Islands, known only from the type locality on Ua Huka in the Hane/Hokatu cliff zone at the head of the valley above Hane village.

Ecology.

Polystichum uahukaense is extremely localized and known from a single population on moist, mossy cliff faces in shade of wet forest with Hibiscus tiliaceus and Pandanus tectorius dominant, at 520-525 m. Associated vegetation on cliffs includes Bidens polycephala Sch. Bip., Boehmeria virgata , Macropiper latifolium (L. f.) Miq., Peperomia pallida (G. Forst.) A. Dietr., Phyllanthus pacificus Müll. Arg., and pteridophyes including Dryopters macropholis , Microsorum grossum (Langsd. & Fisch.) Brownlie, Nephrolepis sp., Pteris comans G. Forst., Selaginella arbuscula (Kaulf.) Spring., and Tectaria jardinii (Mett. ex Kuhn) E. D. Br. The main threats to this ecosystem include rockslides and competition with naturalized plant species including Ageratum conyzoides L., Coffea arabica L., Kyllinga brevifolia Rottb., Oplismenus compositus (L.) P. Beauv., Paspalum conjugatum P. J. Bergius, Psidium guajava L., and Zingiber zerumbet (L.) Sm.

Etymology.

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

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, a single population known; b ( i–iii), habitat continuing decline inferred. The suitable habitat for Polystichum uahukaense on Ua Huka (ca. 83 km2) is indicated as an endangered environment, threatened by feral animals and invasive plants, reducing the extent of the forest. Estimated population size is 300 individuals (Wood 10735).

Specimens examined.

Marquesas Islands: Ua Huka: Hane/Hokatu cliff zone, 520 m, 14 December 2003, K. R. Wood & J.-Y. Meyer 10552 (P, PAP, PTBG, US), 480 m, 8°54'37"S, 139°31'32"W, 12 June 2004, Lorence et al. 9303 (BISH, NY, P, PAP, PTBG, US).

Discussion.

Polystichum uahukaense differs from its Marquesas Islands congeners in having uniformly bipinnate blades, a feature it shares with Polystichum rapense from Rapa Iti which differs in having very dark brown, almost black scales 3-4 mm wide on the rhizome and base of stipe and much smaller, bipinnate fronds (stipes 6-1 cm long, blades 11-14 × 8-10 cm). However, based on overall morphology these two species seem closely allied to each other.

Figures

Figure 7. Polystichum uahukaense Lorence & W. L. Wagner. A rhizome and stipe B blade C detail of stipe with scales D lower surface of sterile pinnule E lower surface of fertile pinnule showing sori and scales F rhizome scale, outline G part of rhizome scale, detail of cells. Drawn from the type collection (Wood 10518) and field images.

Figure 14. A Blechnum pacificum, habit, habit, fertile and sterile fronds (Fatu Hiva, Lorence 6171) B-D Dryopteris macropholis B frond (Ua Huka, Wood 10489, type) C habit, D rhizome and stipe bases (C, D Hiva Oa, Wood 10045) E Polystichum kenwoodii, rhizome and stipe bases (Hiva Oa, Wood 10232) F Polystichum uahukaense, habit (Ua Huka, Wood 10552).