Dicksonia amorosoana Lehnert & Coritico, 2018

Lehnert, M. & Coritico, F. P., 2018, The genus Dicksonia (Dicksoniaceae - Cyatheales) in western Malesia, Blumea 63 (1), pp. 268-278 : 269-271

1. Dicksonia amorosoana Lehnert & Coritico , sp. nov. — Fig. 1 , 2a ; Map 1

A species with long matted woolly hairs on petioles and axes,these forming a uniform cover on the petiole; differing from D. blumei (Kunze) T.Moore in the areolate perispore of the spores (vs smooth and even in D. blumei ) and the absence of stiff hairs protruding from the undercoat. Dicksonia amorosoana differs from D. mollis in lacking bristly irritating hairs on petioles and rachis (vs such hairs present in D. mollis ) and having sori mostly subtended by a sterile lobe (vs sori usually without sterile lobe). — Type: F.P.Coritico FPC 016 (holo PNH-255875; iso BONN (fragment), CMUH-00008374), Philippines, Mindanao, Davao Province, Mt Apo, Kidapawan, North Cotabato, Manda- rangan trail to Lake Venado, N07°01'15" E125°16'30", 2106 m, 5 May 2012.

Etymology. The epithet honours Victor B. Amoroso, eminent Philippine pteridologist.

Tree fern, terrestrial. Trunks to 4 m tall, to 11 cm diam, with persistent petiole bases, frond scars not visible; adventitious buds not observed. Fronds to 210 cm long, held erect to ascending in a funnel-shaped crown. Petioles to 95 cm long (at least 1/3 of frond length), covered throughout with soft, reddish brown to golden, matted hairs, consisting of an outer layer of ciliform hairs to 3 cm long with elongate, turgid to collapsed cells and a dense undercoat of paler tortuous, catenate hairs to 5 mm long; largest hairs with indurated bases, hairs usually already matted and entangled in live plants, only a few protruding, leaving a faintly scabrous surface. Laminae to 120 by 112 cm, tripinnate-pinnatifid, base truncate to cuneate, apex gradually reduced, glossy dark green adaxially and light green abaxially, coriaceous; weakly dimorphic with fertile parts more deeply dissected, occurring throughout the lamina. Frond axes (rachises, costae and costules) abaxially covered with similar hairs as on petioles, with reddish, appressed hairs on rachis, costae and costules, becoming gradually shorter and more bicolorous towards costules, hairs with pale catenate bases and dark brown acicular tips; adaxially hairs sparser, thin and appressed on rachis and proximal costa parts, becoming shorter and more spreading towards costules, here uniformly whitish, curved, to 1.5 mm long. Pinnae subsessile to stalked to 4.5 cm, lanceolate with truncate bases and attenuate tips, alternate, patent, 8–10 pairs per frond, basal pinnae slightly shorter, more than 1/2 the length of longest pinna. Sterile pinnae to 65 by 25 cm; fertile pinnae 20–55 by 8–28 cm. Sterile pinnules to 14.0 by 3.2 cm, lanceolate, subsessile to shortly stalked to 1.3 mm, bases truncate to weakly cuneate, apices attenuate; fertile pinnules to 12.0 by 2.5 cm, elongate-lanceolate, subsessile to stalked to 1.3 mm, bases truncate to weakly cuneate, apices attenuate. Sterile segments to 15 by 5 mm, oblong to linear-lanceolate, deeply pinnatifid to pinnatisect, with rounded lobes, the obtuse apices with crenulate margins; fertile segments to 16 by 5 mm, oblong to linear-lanceolate, pinnatisect to basally pinnate, with acute triangular lobes, each bearing one sorus on the acroscopic arm of a branched vein, the sterile apical section rhomboid with serrate margins. Veins of segments adaxially glabrous, abaxially midveins with bicolorous hairs to 2 mm long, with hyaline catenate bases and dark brown acicular terminal cell, lateral veins with few hairs to 1.5 mm long, spreading, hyaline, pale brown to whitish, thin-walled but usually turgid at base. Sori 1.0– 1.6 mm wide, slightly kidney-shaped when closed, circular when open, mostly (c. 75 %) on end of branched vein, the sterile lobe sticking out weakly to strongly below the sorus, if sorus on simple vein (c. 25 %) then on a lobe that is as wide as or wider than the outer indusial valve; indusia bivalved, outer one greenish with a pale brown cartilaginous margin, inner one light brown with entire margins, both valves may turn darker brown with age or drying but retain a paler margin; paraphyses slightly longer than sporangia, abundant, with red brown clavate tip. Spores tetrahedral-globose, exospore foveate, perispore granulate to baculate, deposited in a retate pattern.

Distribution — Southern Philippines (Mindanao).

Habitat & Ecology — In upper montane forests at c. 2100– 2200 m.

Vernacular name — ‘Amoroso’s woolly tree fern’, suggested herewith.

Additional specimens (paratypes). PHILIPPINES, Mindanao, Davao Province, Lake Linau, Mt Apo , 3 Nov. 1946, Edaño s.n. (UC-750887); Mt Apo , Kidapawan , North Cotabato,within the sampling plot # 9, near Lake Venado , N07°00'07" E125°16'05", 2299 m, 9 Apr. 2013, Silverio FDS 089 (CMUH-00008401) .

Notes — We could only investigate spores from the type, where we found little to no perispore deposited on the exospore. We attribute this to young age and assume that the aspect of fully developed spores will approach the condition seen in D. herberti , D. mollis or D. sciurus C.Chr. ( Fig. 2f ). With the Cyatheales , we often observe variation in the thickness of the perispore layer between different samples of one species, and in the case of the type of D. mollis , we even found spores without perispore (similar to Fig. 2a ) mixed with spores that have it ( Fig. 2e ).

Dicksonia amorosoana is sympatric with D. mollis on Mindanao but usually occurs at higher elevations. It is very different from D. mollis and D. blumei in having all hairs soft and matted, and of an even reddish brown colouration, on frond axes and the petiole. In D. mollis and D. blumei , the hairs on the thicker frond axes are differentiated into a pale, appressed thin undercoat and dark reddish brown to blackish spreading bristles, which in the case of D. mollis tend to have a fragile irritating tip. Dicksonia amorosoana is more similar to D. mollis than to D. blumei regarding the darkened parts of the indusia, the spore morphology and the thickness and orientation of the hairs on the costules. Dicksonia lanigera from New Guinea is another species with a persistent thick shaggy hair cover on petioles and frond axes but is generally smaller than D. amorosoana , with short petioles and basally tapering laminae (petioles to 30 cm long, basal pinnae 1/4 or less of the longest pinnae in D. lanigera vs petioles to 95 cm long, basal pinnae more than 1/2 the length of longest pinna in D. amorosoana ).

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. 1 Dicksonia amorosoana Lehnert & Coritico. a. Detail of petioles with shaggy hairs; b. segments of fertile pinnules, abaxially, showing matted catenate hairs on costa and costules grading into more spreading turgid hairs on midveins; c. sterile pinnules, adaxially. — Photos of the type collection (FPC 016) by F. Coritico.

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.