Dicksonia mollis Holttum

Lehnert, M. & Coritico, F. P., 2018, The genus Dicksonia (Dicksoniaceae - Cyatheales) in western Malesia, Blumea 63 (1), pp. 268-278 : 276-277

5. Dicksonia mollis Holttum — Fig. 2e , 3c , 4c , 6 ; Map 1

Dicksonia mollis Holttum (1962) 64. — Type: A.D.E. Elmer 9874 (holo K-000602588/-000602589; iso BM-000097867, L-0537138/-0537139, MICH-1190338, MO-2675154/-2675155, NY-00127912, P, U-0007357, US-00066376), Philippines, Negros Oriental, Dumaguete, Cuernos Mts , c. N09°15' E123°11', Apr. 1908.

Etymology. The name was chosen because of the softer, denser cover of pale hairs on the costules compared to the similar Dicksonia blumei ; the choice appears rather ironic given that the species has prickly petiole hairs, a feature that D. blumei does not have.

Tree fern, terrestrial. Trunks to 6 m tall, c. 10–12 cm diam, with old petiole bases, old fronds soon falling, not forming skirt around apex; adventitious buds not reported. Fronds to 380 cm long, ascending-arching, few, c. 6–12 per crown. Petioles to 60 cm long, dark brown to blackish, rough with blackish bases of broken-off bristly setiform hairs to 4.5 cm long, dark reddish brown, undercoat of appressed whitish hairs 0.5–1.0 mm long, filiform to catenate, tortuous, undercoat usually not thicker towards petiole base (not counting golden woolly hairs of trunk that may adhere). Laminae to 320 by 130 cm, tripinnate-pinnatifid, coriaceous, ovate-elliptic, widest at the middle, apex gradually reduced, weakly dimorphic with fertile parts more deeply dissected, occurring throughout the lamina. Leaf axes (rachises, costae and costules) dark reddish brown to atropurpureous or blackish, usually paler towards costules, densely hairy, adaxially mainly with curved yellowish white hairs 1.5–2.0 mm long, also with some longer spreading reddish brown hairs, and dense pale undercoat, abaxially with longer spreading reddish brown setiform hairs to 20 mm long, fragile, their blackish bases sticking out of whitish undercoat of flaccid to catenate, tortuous hairs, indument of costae and costules gradually becoming shorter, softer and paler, whitish hairs on costules and midveins usually forming a voluminous cover, relatively few hairs also with reddish tips. Pinnae to 75 by 25 cm, subsessile to short-stalked to 1.5 cm, oblong-lanceolate with attenuate tips, 10–14 pairs per frond, basal pinnae reflexed, c. 2/3 the length of largest pinnae, rarely smaller. Sterile pinnules to 14 by 2.5–3.0 cm, sessile, linear-lanceolate, bases truncate to cuneate, apices attenuate; fertile pinnules to 12.0 by 1.9 cm, sessile, linear-lanceolate, bases cuneate, apices attenuate. Sterile segments to 13.0 by 4.5 mm, oblong to linear, straight to weakly falcate, basal ones free, sessile, otherwise adnate, distal ones decurrent, most segments oblique, coarsely crenate to lobed almost to the midvein, margins crenate to serrate, segment tips rather blunt, acute; fertile segments to 13.0 by 3.5 mm, linear, straight, sessile to adnate with constricted bases, with 5 or 6 pairs of sori, with reduced lamina, sinuses wider than in sterile segments, larger sinuses U-shaped, parallel-sided, segment tips mostly sterile, rhomboid with 2–4 blunt teeth. Veins adaxially glabrous except for sporadic hairs on the midveins, abaxially midveins weakly to densely covered with pale catenate hairs, few to absent on lateral veins. Sori 1.7–2.0 mm diam, oblong when closed, circular when open, mostly (c. 75 %) on simple veins in a lobe that is narrower than outer indusial valve, if sorus on branched vein (c. 25 %) then sterile lobe inconspicuous below sorus; indusia bivalved, outer valve with concolorous pale yellowish brown (rarely darker) cartilaginous margin with notably paler rim, inner valve brown with darkened, sometimes blackish, erose margin; paraphyses longer than sporangia, flaccid to catenate, whitish, with dark brown clavate terminal cell. Spores tetrahedral-globose, to 61 µm diam, exospore foveate, perispore papillate-granulate to baculate, deposited in a retate pattern (‘verrucose’ sensu Holttum 1963).

Distribution — Malaysia (northern Borneo), Indonesia (northern Borneo) and throughout the Philippines.

Habitat & Ecology — At 1500–2000(–2400) m in montane rain forests.

Vernacular name — ‘Philippine bristly tree fern’, ‘porcupine tree fern’, suggested herewith.

Additional specimens. MALAYSIA, Sabah, Mt Kinabalu, E116°32' N06°04', 1828–4100 m, 9 Apr. 1932, Clemens & Clemens 29055 (K, UC); Tenom- pok, 1500 m, 9 Mar. 1932, Clemens & Clemens 29734 (UC); Mt Trusmadi, 2000–2400 m, 10 Apr. 2015, Chen 4279 (TAIF). — PHILIPPINES, Luzon, Camarines Sur, Mt Isarog, Dec. 1928, Edano s.n. (UC); Mindanao, Davao, Todaya (Mt Apo), May 1909, Elmer 10640 (W); ibid., Aug.1909, Elmer 11452 (W); Negros, Balinsasayao twin lake to Guinsayawan, 7 Apr. 2014, Chen 3837 (TAIF). — INDONESIA, Kalimantan, Gunong Besar, c. S02.72 E115.62, 1300–1880 m, 18 Feb. 1979, Murata, Kato & Mogea B 3513 (K).

Notes — Holttum (1962) gives only a short description of D. mollis , stating just the differences to D. blumei . There are ample collections of both species in the major herbaria but almost all of them have no further information about the dimensions of the plants.

The spores of D. mollis are larger than those of the other Malesian species, which is especially noticeable when compared side by side ( Fig. 2 ). This could be an indication of polyploidy ( Barrington et al. 1986) and it should be investigated, with a larger sampling than was possible here, in as much spore size varies within a population depending on plant age and nutrient supply.

Figures

Map 1 Distribution of Dicksonia in western Malesia: D. amorosoana (O), D. blumei (D), D. celebica (Δ), D. ceramica (A), D. mollis () and D. timorensis (z). Map by R. Cámara-Leret.

Fig. 2 Spores of Old World Dicksonia. a. D. amorosoana, distal view, perispore largely lacking, with some mould spore contamination (Philippines, Mindanao); b. D. blumei, distal view, granular persipore filling up retate structure of the exospore (Indonesia, Java); c. D. celebica, proximal view, young spore with perispore only beginning to form near the laesura (Sulawesi, Indonesia); d. D. herberti, distal view (Australia, Queensland); e. D. mollis, distal view (type; Philippines, Mindanao); f. D. sciurus, proximal view (Papua New Guinea) d and f are shown to illustrate the putative fully developed condition of the perispore in a and e, respectively (from: a. Coritico FPC 016, BONN; b. Chen 2040, TAIF; c. Brambach 2036, BONN; d. Kessler 14249, STU; e. Elmer 9874, MICH; f. Lehnert 2886, BONN). — Scale bar: 10 µm.

Fig. 3 Lamina details of Malesian Dicksonia species. a. D. blumei; b. D. celebica; c. D. mollis; a1–c1. sterile pinnules, adaxially (note: a1 from distal part of pinna, b1 and c1 from proximal part of pinna); a2–c2. sterile segments, abaxially; a3–c3. fertile segments, abaxially (from: a. Chen 2040, TAIF; b. Brambach 944, BONN; c. Chen 3837, TAIF).

Fig. 4 Petioles and axes of Malesian Dicksonia. a. D. blumei; b. D. celebica; c. D. mollis; first row (a1–c1) axils between rachis and costa, abaxially; second row (a 2 –c 2) details of petioles, a 2 with hairs partially abraded, exposing the epidermis and the paler softer undercoat, c 2 with most hairs broken off on the right side (from: a. Chen 2040, TAIF; b. Brambach 944, BONN; c. Chen 3837, TAIF).

Fig. 6 Dicksonia mollis Holttum. a. Trunk apex, showing petioles with stiffly spreading hairs, exposing the thin matted yellowish undercoat; b. fertile pinnules, abaxially, showing thin cover of matted catenate hairs with some darker hairs protruding from costa, while on the costules there is a more uniformly pale brown cover of antrorsely curved hairs. — Photos by F. Coritico.