Dicksonia thyrsopteroides Mettenius (1861: 81)

Noben, Sarah & Lehnert, Marcus, 2013, The genus Dicksonia (Dicksoniaceae) in the western Pacific, Phytotaxa 155 (1), pp. 23-34 : 32-33

Dicksonia thyrsopteroides Mettenius (1861: 81) . ( Figs. 2D , 3D )

Type:— NEW CALEDONIA. Province du Nord: Balade, [ca. 20°18'41"S, 164°30" E,] 1855, Vieillard 1634 (holotype P) .

Trunks to 3 m tall, to 10 cm diameter, with old petiole bases, without skirt of old fronds. Adventitious buds not reported. Fronds to 150 cm long, ascending-arching, strongly hemidimorphic. Petioles to 34 cm long, light brown to dark brown, smooth to slightly rough with a sooty undercoat at the base, covered with setiform, reddish to dark brown hairs to 2.5 cm long, hairs glabrescent, only persistent at petiole bases. Laminae to 100 × 150 cm, tripinnate-pinnatifid, firm herbaceous, gradually reduced apically, widest pinnae at the middle, the basal pinnae sterile, middle/central pinnae fertile, distal pinnae sterile. Leaf axes [rachises, costae and costules] abaxially glabrous or with few to many reddish, catenate hairs, more in the axils of pinnae and pinnules, adaxially covered with pale to reddish, short ciliate hairs. Veins glabrous or main vein weakly to strongly hairy; hairs whitish to reddish. Pinnae subsessile to sessile, oblong-lanceolate with attenuate tips, 10– 14 pairs per frond. Sterile pinnae to 47 × 16 cm; fertile pinnae up to 50 × 27 cm. Sterile pinnules to 9-10 cm × 1.7–1.9 cm, oblong-lanceolate, basal auriculate; Fertile pinnules to 14 × 3.5 cm, oblong, sessile. Fertile segments reduced to thin strands along the veins, sessile; sterile segments weakly lobed or dissected, margins serrate, sessile. Sori 1.7–2.0 mm wide, oblong to slightly kidney shaped when closed, circular when open, at the end of unbranched lateral veins, costal, indusia bivalved, outer one dark brownish, with cartilaginous margin, inner one light brown with slightly undulate margins; paraphyses longer than sporangia. Spores tetrahedral-globose with prolonged, depressed lobes, 45 × 57 µm, exospore smooth, perispore bacillargranular.

Distribution and habitat: —Restricted to northern and western New Caledonia, in evergreen mountain rainforest at (300–) 500–950 m, absent from ultramafic soils ( Fig. 1B, F ).

Etymology: —The name refers to the similarity of the hemidimorphic fertile fronds with those of Thyrsopteris elegans Kunze (1834: 507) from the Juan Fernández Islands.

Additional specimens examined: — NEW CALEDONIA. Province du Nord: Canala, [ca. 21°31'10''S, 165°57'11'' E,] 600 m, 20 November 1869, Balansa 1597a ( P); Koindé , 21°37'S, 165°57'E, 520 m, 22 November 1977, P . Bamps ( P); Col de Parari , [ca. 20°19'59''S, 164°28'52''E,] 11 June 1956, H. S . Mackee 4767 ( P); crête au N de la Haute Pouéo ( 14 km E du Col des Rousettes ), [ca. 21°25'30"S, 165°34'15"E,] 500 m, 27 December 1962, H. S . Mackee 9849 ( P); Valee d’Amoa , exploitation forestière Letocart, [20°54'55''S, 165°17'40''E,] 300–500 m, 12 August 1965, H. S . Mackee 13234 ( P); Mont Panié , 20°37'22''S, 164°44'40''E, 08 April 2006, J . Munziger et al. 3404 ( MO, P, NSW, NOU n.v.); Col d’Amos, 20°18'S, 164°26'E, 550 m, 29 April 1996, J. C . Pintaud & J. P . Tivolier 345 ( P); Route forestière au Col des Rousettes (sol ferrallitique lessivé), 30 June 1965, M . Schmid 364 ( P); Mont Colnett , [ca. 20°30'S, 164°42'E,] 950 m, 1 November 2004, U. G . Swenson et al. 624 ( MO, S); Mont Panié , 20°37'22''S, 164°44'40''E, 550 m, 24 October 1999, H . van der Werff & G . McPherson 15921 ( MO) .

Discussion: — Dicksonia thyrsopteroides is easily delimited from D. baudouinii by the different laminar morphology (hemidimorphic with sessile pinnae and strongly reduced laminar tissue in fertile segments in D. thyrsopteroides vs. holodimorphic fronds, stalked pinnae and weakly reduced laminar tissue in fertile segments in D. baudouini ). Some specimens previously included in D. thyrsopteroides are here placed in the newly described species D. perriei or D. munzingeri , which see for discussion.

Another species similar to Dicksonia thyrsopteroides is D.brackenridgei from Fiji, Samoa and Vanuatu, which has also hemidimorphic fronds with fertile segments reduced to the veins, and a sooty undercoat on petioles. However, D. brackenridgei has at least basally stalked pinnae (vs. all sessile) and ephemeral pale brown wooly hairs with persistent dark brown indurated bases that leave a scabrous surface on the petiole, similar to D. baudouinii . Concerning the petiole hairs, D. thyrsopteroides is somewhat intermediate between the other two mentioned species, with soft but not matted, spreading to appressed hairs that vary between pale brown (as predominant in D. brackenridgei ) from the petiole bases to reddish brown (as predominant in D. baudouinii ) in the more distal parts.

Key to the species of Dicksonia on the western Pacific Islands

1. Pinnae stalked; petiole hairs at least partially spreading and persistent up to the lower rhachis, leaving a scabrous surface when abraded; undercoat absent or inconspicuous .......................................................................................... 2

–. Pinnae sessile to subsessile; petiole hairs if spreading, only persistent near the base, leaving a smooth surface, undercoat of fine matted hairs present, sooty to white, conspicuous [unfurling crozier completely covered in hairs but glabrescent]. ( New Caledonia) ............................................................................................................................... 3

2. Fronds holodimorphic, the partially skeletonized fertile areas may occur from laminar base to apex; petiole hairs reddish brown and bristly, also some softer golden hairs in the axils towards the trunk, no differentiated undercoat; sori 1–2 mm in diameter; veins abaxially with hairs, few and scattered. ( New Caledonia)................... D. baudouinii

–. Fronds hemidimorphic, the fully skeletonized fertile areas may occur from laminar base to the center; petiole hairs dark brown and spreading, originally with softer pale brown tips, these often matted prior to wearing off, the bases bristly to slightly irritating, also some softer whitish hairs in the axils towards the trunk, dark brown to sooty undercoat present but inconspicuous; sori 1.0– 1.5 mm in diameter; veins abaxially without hairs. ( Fiji, Samoa, Vanuatu) ........................................................................................................................................... D. brackenridgei

3. Trunks to 10 cm diameter, fertile plants usually with discernable trunk; sooty undercoat on petioles; petiole hairs reddish brown, spreading, persistent only near the base, here also becoming paler, golden to whitish; costae adaxially glabrescent with scattered hairs ....................................................................................... D. thyrsopteroides

–. Trunks to 20 cm diameter, fertile plants may be trunkless; undercoat on petioles not sooty but white to pale brown or orange-brown; longer petiole hairs if present not spreading but matted; costae adaxially with a line of matted hairs.. ..................................................................................................................................................................................... 4

4. Longer petiole hairs white to grey, sometimes with brown tips, matted, falling off in flakes that mimic scales; undercoat white to greyish, on croziers also partially brown ................................................. D. munzingeri , sp. nov.

–. Petiole hairs yellowish to orange, matted, forming a velvety cover that is easily abraded; undercoat not differentiated ........................................................................................................................................................ D. perriei , sp. nov.

Figures

FIGURE 1. Distribution of Dicksonia species on New Caledonia related to precipitation and geology: A. Precipitation; 1500 mm/a isohyet delimits rain forest vegetation, 3000 mm/a isohyet delimit centers of endemism (fide Pintaud et al. 2001); basemap modified from commons.wikimedia.org. B. Geology (© http://runswithrocks.wordpress.com). C. Dicksonia baudouinii. D. Dicksonia perriei, sp. nov. E. Dicksonia munzingeri, sp. nov. F. Dicksonia thyrsopteroides. (Basemap © d-maps.com)

FIGURE 2. Morphological features of New Caledonian Dicksonia species: First row (1) sterile (A, C & D) or intermediate segments (B), abaxially; second row (2) fertile segments, adaxially; third row (3) petioles. A. Dicksonia baudouinii. B. Dicksonia perriei, sp. nov. C. Dicksonia munzingeri, sp. nov. D. Dicksonia thyrsopteroides.

FIGURE 3. Morphological features of New Caledonian Dicksonia species: sterile pinnules, adaxially A. Dicksonia baudouinii. B. Dicksonia perriei, sp. nov. C. Dicksonia munzingeri, sp. nov. D. Dicksonia thyrsopteroides.