Janssen, Janssen & Rakotondrainibe, 2008

Janssen, Thomas & Rakotondrainibe, France, 2008, A revision of the indusiate scaly tree ferns (Cyatheaceae, Cyathea subgen. Alsophila sect. Alsophila) in Madagascar, the Comoros and the Seychelles, Adansonia (3) 30 (2), pp. 221-376 : 348-352

40. Cyathea sechellarum Mett.

( Figs 40 ; 53B )

Annales Musei Botanici Lugduno-Batavi 1: 58 (1863); Baker, Flora of Mauritius and the Seychelles: 467 (1877); Christensen, Transactions of the Linnean Society of London, 2nd ser., Botany 7: 412 (1912); Tardieu, Notulae Systematicae 16: 156 (1960). — Alsophila sechellarum (Mett.) R.M.Tryon, Contributions from the Gray herbarium 200: 31 (1970). — Type: Îles Seychelles, 1841, Pervillé 76a (lecto-, L! [L0597849], here designated; isolecto-, B!, G!, K!, P!). — Seychelles, Mahé, Morne Seychellois National Park, summit of Morne Blanc, 04°39’24’’S, 55°25’59’’E, 650 m, Janssen et al. 3226 (epi-, P! [3 sheets: P00589647-49], here designated; isoepi-, MO!, P! [3 sheets], SEY!)

ADDITIONAL MATERIAL EXAMINED. — Seychelles. Boivin s.n. (P). — Bouton 2072 (BM). — Lister s.n. (BM). — 1841, Pervillé s.n. (P[3], K). — Pervillé 356bis (L, paralectotype). — S. coll. 38 (P). — S. coll. s.n. (B, K) .

Mahé, Barkly s.n. (BM). — Bois des hauts, IV.1848, Boivin s.n. (P). — 25.II.1909, Gardiner s.n. (K). — IX.1846, Horne 203 (B). — IX.1871, Horne 203 (K). — Humblot 48 (P), 158 (P). — Casse Dent, 04°38’S, 55°26’E, 600 m, 17.XI.2006, Janssen et al. 3201 (MO, P, SEY). — Idem, 650 m, Janssen et al. 3213 (G, MO, P, SEY). — Vingt Cinq Sous (NE Morne Jasmin), 04°37’S, 55°24’E, 450 m, Janssen et al. 3247 (G, MO, P, SEY). — Morne Sechellois, 8.XI.1961, Jeffrey 426 (K, P, SEY). — 1903, Merian s.n. (P). — 20.II.1840, Pervillé 88 (P), 90 (P). — 7.III.1840, Pervillé 156 (P). — 27.II.1882, Thiebaut 48 (P). — Chemin allant de Port Victoria à la Forêt Noire, II.1876, s. coll. s.n. (P[2]).

Silhouette, Gardiner s.n. (K).

FIELD OBSERVATIONS. — Trunk: HT up to 2(-5) m, DT 7-9 cm excluding, or 11-12 cm including the persistent petiole bases which often retain their scales, leaf scars usually concealed; trunk surface blackish brown, coarsely muricate; trunk base often thickened by rather laxly interwoven adventitious roots.

Petiole: with one row of white to light brown, close standing aerophores, 0.5-2 cm long, on either side; petiole bases sigmoid in young, almost straight in older plants.

Leaf scars: about 2 × 3 cm, ovate, not raised, spirally arranged.

Crown: with long, more ore less erect petioles and widely arching rachises in young plants; with short petioles and spreading more or less horizontally in older plants.

Trunk apex: densely scaly, visible through the petiole bases.

Lamina: ovate to elliptic; LL 180 cm, WL 100-130 cm, FW 70-90 cm, NP 10-13.

DESCRIPTION

Petiole: 25-100 cm long, 3-4 cm in diameter; green to dark brown, abaxially sometimes reddish or almost black, distantly and sharply muricate, bearing a thin, light brown, caducous squamulate tomentum; 1 or 2 pairs of reduced pinnae, (10-) 15- 21 cm long, at (5-) 15-25 cm from the petiole base, usually decaying well before the rest of the leaf, very rarely absent.

Lamina: bipinnate-pinnatisect to tripinnate, subcoriaceous, often only sparsely fertile, fertile-sterile dimorphism absent; shiny dark green above, dull light green to somewhat glaucous below, lamina base shortly attenuate, basal pinnae patent and more or less conduplicate; rachis of the same colour as the petiole, becoming more or less green distally, very sparsely muricate.

Largest pinnae: up to 65 cm long, distant by 11- 15(-18) cm, adjacent pinnae overlapping; costae and costulae green to light brown, distantly muricate.

Largest pinnules: 8-11 × (1-)1.5-2(-2.5) cm, adjacent pinnules slightly overlapping or distant, linear-oblong, their apex caudate; divided to the costula into broadly adnate segments, adjacent segments confluent from below the middle of the pinnules; pinnule segments 0.2-0.3 cm wide, spaced by less than their width, falciform, usually with a distinctly serrulate margin, apex acute; lateral veins in the segments once furcate.

Scales and hairs: scales present from the petiole base upwards to 40(-80) cm on the petiole, at its base imbricate, but usually not very dense, more or less caducous, narrowly triangular, (2-)2.5-3 × 0.2- 0.3 cm, straight, with a slightly twisted and crispate apex, shiny light to dark brown, concolourous or with a slightly lighter margin, more or less appressed, but their apex usually recurved and patent to antrorse, conspicuously indurated at their point of attachment; light brown, broadly deltoid scales, up to 1.5 mm long, one cell layer thick and soft, with an irregular, long ciliate margin on the costulae and midveins of the segments, density variable according to the age of the leaf, a long apical hair may, in young scales, exceed the length of the scale body; filiform, crispate and branched, hair-like scales present on the midveins of the segments; adaxial face of the rachis and costae with scattered filiform scales and densely tomentose with light brown to stramineous, contorted to antrorse, multicellular hairs; adaxial face of the costulae with scattered hairs only.

Sori: very close to the midvein, contiguous, up to 0.1 cm in diameter, covering the entire pinnule segment, but usually restricted to its lower half; indusia shallowly cup-shaped, brown, subcoriaceous, at maturity with an entire to undulate-crenate rim, sometimes breaking up down to the base of the receptacle; receptacle columnar, distinctly longer than the rim of mature indusia, with inconspicuous filiform paraphyses shorter than the sporangia.

DISTRIBUTION

Seychelles: Mahé and Silhouette islands; endemic.

ECOLOGY

300-900 m. Dense evergreen rain- and cloud forests as well as on forest margins. Usually not forming large populations.

REMARKS

Fragmentary material of this species is very near C.boivinii s.l. (Tardieu-Blot 1960)and C.dregei from Madagascar as well as to C. excelsa from the Mascarenes. Cyathea sechellarum differs from C. boivinii chiefly by its shorter and basally indurated petiole scales, the abundant scaly indument on the abaxial face of the costae and costulae and the absence of a fertile-sterile dimorphism.Furthermore, the margin of the segments of C. sechellarum is finely serrulate, while it is entire or crenulate in C. bovinii s.l. Cyathea sechellarum is distinct from C. dregei by its shorter and basally indurated petiole scales, larger pinnae and shallowly cup-shaped indusia with an entire rim at maturity. Cyathea excelsa has globular indusia, lacks reduced pinnae near the petiole base and has longer and denser petiole scales. In addition, the crown of C. sechellarum is usually smaller than in all of the aforementioned species to the exception of C. dregei . Cyathea sechellarum is very near C. boivinii var. hildebrandtii from Madagascar and the Comoros, which has broader, longer and darker petiole scales, pinnule segments with a rounded to obtuse apex and subentire margin, very sparse or lacking soft, light brown ap- pressed scales on the abaxial face of the costulae and midveins and a thicker trunk and larger crown.

Although young plants have been encountered and a considerable number of plants have been observed in the Morne Sechellois National Park, the species should be regarded as highly threatened due to its small area of distribution.

TYPIFICATION AND SYNONYMY

Pervillé 76a is a widely distributed collection. The specimen in “Herb. Lugd.-Bat.” carrying Mettenius’ handwriting (L, L0597849) consists of a fertile middle pinna and is chosen here as the lectotype. Its syntype, Pervillé 356bis, corresponds to a leaf apex and has been traced in L only. The original material lacks petioles and we consider it necessary to designate an epitype including the characteristic scales and reduced basal pinnae to provide an unambiguous definition of this taxon.

Figures

FIG. 40. — Cyathea sechellarum Mett.: A, pinnules abaxially with a fragment of the costa, sori omitted from one pinnule; B, sori, note the cup-shaped indusium and scaly indument on the segment midvein; C, habit (left: adult plant; right: young plant); D, pinnule segments abaxially with a fragment of the costula; E, filiform scale from the abaxial face of a segment midvein; F, deltoid scale from the abaxial face of a segment midvein; G, basal part of the leaf (from the petiole base up to the first pinna pair), lateral view, one half of the petiole pruned away by longitudinal section, note presence of a pair of reduced pinnae near the base of the petiole; H, scale from the base of the petiole; I, leaf scars and trunk surface, persistent dead petiole bases (above) removed from two scars (below). A, B, D, G, H, Janssen et al. 3226 (P); C (left), Janssen et al. 3247 (P), C (right), uncollected, photograph at P; E, F, Janssen et al. 3247 (P); I, Janssen et al. 3201 (P). Scale bars: A, G, 5 cm; B, 0.1 cm; C, 1 m; D, H, 0.5 cm; E, F, 0.5 mm; I, 1 cm.

FIG. 53. — Photographic documentation of field characters in Cyathea: A-D, habit; A’-D’, trunk apex; A”-D”, trunk surface at breast height; A-A”, Cyathea melleri (Baker) Domin; B-B”, C. sechellarum Mett.; C-C”, C. similis C.Chr.; D-D”, C. valdesquamata Janssen & Rakotondr. A, A’, B’, B”, uncollected; A”, Janssen et al. 2569; B, Janssen et al. 3247; C, Janssen et al. 2402; C’, Janssen et al. 2576; C”, Janssen et al. 2393; D, D”, Janssen et al. 2907; D’, Janssen et al. 2904. Vouchers at P. Photos A’-A”, C’ by G. Rouhan (MNHN); all other photos by T. Janssen. Scale bars: A-D, 1 m; A’-D’, A”-D”, 10 cm.