Dicksonia utteridgei Lehnert& Cámara-Leret, 2018

Lehnert, M. & Cámara-Leret, R., 2018, Dicksonia utteridgei, a new species of hairy tree fern (Dicksoniaceae - Cyatheales) from New Guinea, Blumea 63 (2), pp. 140-143 : 140-143

Dicksonia utteridgei Lehnert& Cámara-Leret , sp. nov. — Fig. 1 , Map 1

A newly recognized species of Dicksonia with bristly reddish to dark brown hairs on petioles and rachises, and large ovate-lanceolate to triangular pinnules, which are notably stalked and themselves fully pinnate to bipinnate-pinnatifid, with the largest segments clearly stalked.All other known species of Dicksonia are at most fully pinnate at the base of the pinnules, and even then the basal segments are sessile. — Type: P.J. Edwards 4370 with R.J. Johns, A. Hidayat, P. Rudall, D. Tekege, T.M.A. Utteridge, F.R. Willis (holo K 18 sheets; iso BO), Indonesia, Papua [Irian Jaya],Freeport Concession Area, ridge next to main road,about 1 km above Tembagapura, 2300 m, 3Apr.1999.

Etymology. Named for Timothy M.A. Utteridge,head of Identification and Naming Department at The Royal Botanic Gardens Kew, in recognition of his work to promote botanical knowledge and the floristic exploration of New Guinea.

Tree fern, terrestrial. Trunks 1.4 m tall; vascular tissue solenostelic; 8–10 cm diam, covered in old, blackish petiole bases, these sticking out between the brown hairs and adventitious roots, without skirt of old fronds; adventitious buds presumably regular, type plant with three separate crowns departing from main trunk at 0.8 m above ground. Fronds to c. 360 cm long, with ascending petioles and arching to distally drooping blades. Petioles 60–90 cm long, dark brown to black, covered with setiform, reddish to dark brown hairs to 2.5 cm long, stiffly spreading, hairs dense at base but thinning in most parts of the petiole, persistent at bases, cinnamon-brown undercoat of matted tortuous, at least partially catenate hairs, extending from petiole base through all frond axes, soon worn off in exposed parts. Laminae to c. 270 by 150 cm, coriaceous, glossy dark green adaxially, subglossy olive-green abaxially, tripinnate-pinnatifid to quadripinnate-pinnatifid, elliptic, gradu- ally reduced apically, widest pinnae at the middle, the basal pinnae c. 1/3 the length of the longest pinnae, not reflexed; weakly dimorphic, fertile parts with slightly reduced green tissue, occurring patchily in central and lower parts. Leaf axes (rachises, costae and costules) with easily worn-off coat of matted hairs like on the petiole, remaining longest in the axils of pinnae and pinnules, epidermis shiny blackish brown where exposed, scabrous to verrucose with bases of abraded larger hairs. Pinnae to 77 by 36 cm, subsessile to short-stalked 1 .0–1.5 cm, oblong-lanceolate with attenuate tips, with basal basiscopic pinnules much reduced, c. 10 pinna pairs per frond. Largest pinnules to 19.0 by 9.5 cm, stalked to 1.4 cm, ovate-lanceolate to triangular, basally ± truncate to weakly cordate with segments weakly reflexed, apically long-acute to attenuate. Segments to 45 by 15 mm, free and short stalked to 2 mm except for pinnule tip, oblong to elongate with obtuse to rounded tips, pinnatifid to (almost) pinnate basally, free lobes patent, adnate lobes oblique; sterile segments with weakly revolute crenate margins, lobes appearing subentire or entire; fertile segments more deeply incised between the sori, the lobe tips often more deeply crenate than those of sterile segments. Veins prominent on both sides, midveins of segments and lobes ridged adaxially, veins glabrous except for segment midveins, adaxially with antrorsely curved, dark reddish hairs to 1.0 mm long, abaxially hairs softer, originally denser but also more ephemeral, antrorsely curved to matted, to 1.5 mm long. Sori 1.5–2.0 mm wide, 1 or 2 (or 3) pairs per lobe, kidney-shaped when closed, ± round when opened, at the end of unbranched lateral veins; indusia bivalved, outer one greenish to brownish, with dark brown cartilaginous margin, inner one dark brown with slightly erose margins and some hyaline cells; paraphyses longer than sporangia, catenate, tortuous, whitish, hyaline, with a red clavate tip. Spores white to pale yellow, with reticulate perispore; ultrastructure not investigated.

Distribution — Only known from the type locality in central New Guinea (Prov. Papua, Indonesia).

Habitat & Ecology — Only known from stunted ridge top forests at 2300 m.

Vernacular name — ‘Utteridge’s rough tree fern’, suggested herewith.

Notes — The type of this new species contains a section of the trunk, which shows unmistakably vascular tissue arranged in a solenostele, putatively amphiphloic (= siphonostele). The same type is documented for the non-aborescent Dicksoniaceae genera Calochlaena and Lophosoria , but not for Dicksonia . Here the vascular tissue is generally described as corrugated dictyostele ( Bower 1926, Kramer 1990), based mainly on observations on the Australo-American clade sensu Noben et al. (2017), e.g., D. sellowiana Hook. ( Tryon & Tryon 1982) and D. antarctica Labill. , which is traded for horticulture as cut trunks ( Hoshizaki & Moran 2001). This corrugated dictyostele can be interpreted as solenostele with more tightly packed leaf traces: D. antarctica has fronds in distinct whorls in short distance whereas D. utteridgei supposedly has them in a wider spiral around the trunk, as observed in most New Guinean taxa. A complete survey of trunk sections may reveal a phylogenetic signal in the development of the stele type.

Among the New Guinean Dicksonia , D. utteridgei is regarded a close ally of D. archboldii Copel. based on the dark axes, the stiff, brittle red petiole hairs and the thick cinnamon brown undercoat. Petiole material alone would be indistinguishable but D. utteridgei has a unique laminar dissection ( Fig. 1 ); much more strongly divided (tripinnate-pinnatifid to quadripinnate-pinnatifid vs bipinnate-pinnatifid to tripinnate) and with blunter ultimate segments (vs tips acute, in fertile segments coarsely serrate).

Dicksonia utteridgei is currently only known from the Mt Jaya region, where it grows near two species that are more widespread on the island, the already mentioned D. archboldii as well as D. lanigera Holttum ( Map 1 ). At Mt Jaya, D. archboldii grows between 2 175–3 800 m, from mid-montane forests to subalpine shrubbery, and D. lanigera grows on vertical limestone cliffs at c. 3 100 m (Johns 10721, K) but can also be found in forest clearings. Dicksonia lanigera cannot be confused with D. utteridgei as it differs in all diagnostic characters, having only soft, usually matted reddish hair, basally tapering blades, sessile pinnae and pinnules, green to brown but never notably darkened frond axes, and smaller sori (c. 1 mm wide).

The other New Guinean species with dark axes are easily separated from D. utteridgei (as well as from D. archboldii ) either by size and shape of the fronds (e.g., fronds <200 cm long, pinnae strongly tapering basally, petiole short in D. hieronymi Brause ) or by the absence of stiff spreading hairs (e.g., only soft matted cinnamon brown hairs in D. grandis Rosenst. ).

From the lamina colour, texture and dissection of the penultimate segments, D. utteridgei is very similar to D. arborescens L’Hér. from St. Helena Island; smaller pinnules of D. arborescens may look very much like larger tertiary segments of D. utteridgei . This similarity is particularly interesting considering the fact that in the latest phylogeny ( Noben et al. 2017), all hitherto described New Guinean Dicksonia species are resolved as crown group in a clade to which D. arborescens and the endemics from Juan

d

Fernández form the sister taxon, with the remaining Australian (i.e., D. herberti W.Hill , D. youngiae C.Moore ex Baker ) and western Malesian taxa (i.e., D. blumei (Kunze) T.Moore , D. mollis Holttum , etc.) are resolved as paraphylum between them. The addition of D. utteridgei to the phylogeny could change the ancestral area reconstruction if it does not group with the other New Guinean species but instead more closely to D. arborescens . If both were resolved as sister species, as morphology suggests, it would imply a relatively recent long distance dispersal between New Guinea and St Helena over several thousand kilometres without settling in other areas of suitable vegetation found in between. Currently, it seems most plausible to postulate an ancestral trans-Antarctic distribution of this group (the Malesian clade sensu Noben et al. 2017), which got fragmented by the glaciation of Antarctica that started by the end of the Eocene (c. 35 Mya) and was complete by the mid-Miocene (c. 15 Mya). The Australian population would have given rise to the remainder of the Malesian species, while the South American population would have spread to the neigh- bouring oceanic islands (age 15–5 My) before going extinct on the mainland ( Noben et al. 2017). In the same timeframe falls the split between Old World and New World taxa of the Australo-American clade ( Noben et al. 2017).

Figures

Map 1 Distribution of Dicksonia archboldii Copel. (Δ), D. lanigera Holttum (Z) and D. utteridgei Lehnert & Cámara-Leret (✩) in the Mt Jaya region, Papua province, Indonesia.

Fig. 1 Dicksonia utteridgei Lehnert & Cámara-Leret.a. Petiole;b. medial pinna (c. 56 cm long), mostly sterile,arrows indicate pinnules that are partially fertile; c. sterile tertiary segment abaxially; d. fertile tertiary segment abaxially (P.J. Edwards 4370 (holo), K). — Drawing by M. Lehnert (BONN), 2017.