Dryopteris sweetorum 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 : 12-13

3. Dryopteris sweetorum Lorence & W. L. Wagner sp. nov. Fig. 5

Latin.

A D. macropholi minoribus, atro-castaneis, ovato-lanceolatis vel lineari-oblongis squamis 12-25 × 1.5-2 mm supra rhizomates et stipitum bases, largis tripinnato-pinnatifidibus frondibus, ultimis segmentibus usque ad 15 × 5 mm, intervallibus 5-10 mm distantibus, obliquis, acutis culminibus, sectis ca. in medio ad costulam cum marginibus acute serratis, abaxialibus superficiebus et glabris rachidibus differt.

Type.

Marquesas Islands: Fatu Hiva: Teavapuhiau, ridge to Touaouoho, 2000 ft (607 m), 8 September 1995, K. R. Wood 4493(Holotype: PTBG-038471!, PTBG-038472!, PTBG-038473!, PTBG-0384741! [4 sheets]; Isotypes BISH! [2 sheets], P!, PAP! [3 sheets], NY!, US! [3 sheets]).

Description.

Terrestrial ferns; rhizomes short creeping to suberect, 3-15 cm in diameter including stipe bases, densely clothed with scales; scales of rhizomes and bases of stipes lustrous, dark brown, 9-25 × 1-2 mm, ovate-lanceolate to linear-oblong, concolorous, margins entire to subentire distally with short, irregular teeth, cells linear. Fronds densely clustered, 5-7 per rhizome; stipes (45 –)60– 100 cm long, 7-10 mm in diameter medially, adaxially grooved, stramineous to medium brown, densely scaly basally, distally with progressively smaller scales and appressed hairlike scales, mostly glabrescent, surfaces brown-punctuate; blades firmly chartaceous, broadly ovate-deltate, (42 –)62– 93 × (38 –)64– 80 cm, 3-pinnate-pinnatifid at base, otherwise mostly 2-pinnate-pinnatifid, with pinnae opposite to subopposite, spreading, 8-13 on a side; rachises stramineous, with scattered narrow scales to 2-12 × 0.2-0.6 mm; lowermost pinnae the largest, 25-38 × 19-25 cm, slightly inequilateral, basiscopic basal pinnules 10-15 cm long, acroscopic basal pinnules slightly shorter, 7-12 cm long, distal pinnae stalked to 5 mm or sessile, apex pinnatifid; ultimate pinnules to 15 × 5 mm, spaced 5-10 mm distant, oblique, tips acute, cut ca. ½ toward costule, with margins acutely serrate, adaxially glabrous, abaxially glabrous or rachises with scattered hairlike scales; veins forking, scarcely visible adaxially, prominulous abaxially. Sori (1 –)3– 6 pairs per segment, supramedial; indusia 0.9-1.3 mm in diameter, brown, thick, glabrous except with a few short-stipitate glands in center. Spores dark brown.

Distribution.

Known only from Fatu Hiva, Marquesas Islands, in montane wet forest at 600-640 m elevation.

Ecology.

This new endemic species is apparently rare and localized, known only from the region from Teavapuhiau ridge to Mt. Touaouoho where it grows scattered among other ferns on hillsides in understory of open forest with Alsophila tahitensis , Crossostylis biflora , Cyclophyllum barbatum (G. Forst.) N. Hallé & J. Florence, Freycinetia impavida , Hibiscus tiliaceus , Metrosideros collina , Pandanus sp., Weinmannia marquesana var. marquesana, and Vaccinium cereum var. adenandrum, and Wikstroemia coriacea Seem.

Etymology.

We take great pleasure in naming this magnificent new species in honor of Barbara K. and Cyrus B. Sweet, III, who have generously supported scientific research at the National Tropical Botanical Garden and particularly the Vascular Flora of the Marquesas Islands project.

Discussion.

This new species differs from Dryopteris macropholis by the characters noted in the diagnosis above, notably in the ultimate pinnules segments spaced 5-10 mm distant with serrate margins and acute apices.

Conservation status.

Proposed IUCN Red List Category: Critically Endangered (CR): B1ab, B2a,b ( i–iii). B1, total extent of occurrence less than 100 km2 (ca. 85 km2), a,b, known from a single location; B2a, estimated area of occupancy estimated to be less than 10 km2 [three collections likely representing a single population are known]; B2b ( i–iii), habitat continuing decline inferred. The estimated area of occupancy for Dryopteris sweetorum on Fatu Hiva (less than 10 km2) is indicated as an endangered environment, threatened by human activity (deforestation and fire), feral animals, and invasive plant species, reducing the extent of the forest.

Specimens examined.

Marquesas Islands: Fatu Hiva: Teavapuhiau, leeward side of windswept ridge, UTM 758470-8840707, 2100 ft (640 m), Wood 10091 (PTBG [3 sheets], PAP [2 sheets], US [3 sheets]); Teavapuhiau Pass (above Ouia Valley), 70 0 m, B. Gagné 1233 (US); Epaulement SW de Mt. Touaouoho, 770 m, 10°29'S, 138°38'W, Florence et al. 9536(P [4 sheets]).

Figures

Figure 5. Dryopteris sweetorum Lorence & W. L. Wagner. A stipe and part of rhizome B blade C detail of stipe with scales D lower surface of fertile pinnule showing sori E rhizome scale F part of rhizome scale, detail of cells. Drawn from the type collection (Wood 4493) and field images.