Oncophorus elongatus (I.Hagen) Hedenas

1. Oncophorus elongatus (I.Hagen) Hedenäs Fig. 6

Lindbergia 30: 36 (Hedenäs 2005). – Oncophorus wahlenbergii var. elongatus I.Hagen, TromsØ Museums Aarshefter 21–22: 13 (Hagen 1899). – Cynodontium wahlenbergii var. elongatum (I.Hagen) Mönk., Die Laubmoose Europas: 195 (Mönkemeyer 1927). – Type: “Norway. Nordland, Saltdalen, Rognanfjeld, 67º 6′ N, 600 m asl, 21 July 1889, R. E. Fridtz” (lecto-: O!, designated by Hedenäs 2005).

Plants up to ten cm high, mostly in loose tufts, green or yellow-green. Stem with large central strand, a cortex plus epidermis of 1–2 layers of incrassate cells, epidermis not differentiated as a hyalodermis; axillary hairs with 2–8-celled, hyaline upper portion, 8–10 µm wide, basal 1–2 cells rectangular, brown; rhizoids strongly branched, red-brown, smooth, in leaf axils or shortly above. Leaves 2.5–6.4 × 0.4– 1.2 mm, when moist from strongly sheathing base erect, or erect-patent to spreading and straight or slightly curved, when dry with middle leaf spreading and gradually curved upwards or upwards-inwards and curled or slightly curled, from oblong-obovate or ovate sheathing portion (narrowed or strongly narrowed towards insertion) with long and almost linear, gradually narrowing upper portion, apex long- or very long-acuminate; leaf margin plane throughout, below entire, in upper 20–25(–35)% partly irregularly dentate or denticulate with sharp forwards-directed teeth, or sometimes relatively weakly denticulate, or some leaves almost entire and other leaves with scattered teeth along upper margin, teeth single or occasionally double, sometimes with cell walls projecting along upper margin, margin varying from unistratose to bistratose; costa 53–125 µm wide near base, with dorsal and ventral epidermis cells slightly widened but incrassate, one layer of large guide cells, 1–3 layers of ventral stereids and 2–3(–4) layers of dorsal stereids, sometimes with mammillae, or erect to forwards-directed teeth on upper back; lamina cells in acumen incrassate or strongly so, 10–21 × 9–14 µm, 0.9–2.0 times as long as wide, in mid-leaf incrassate or strongly so, 11–29 × 8–13 µm, 1–3 times as long as wide, and in sheathing lamina strongly incrassate and eporose or indistinctly porose, 36–88 × 8–14 µm, 3.5–9.1 times as long as wide, transition between mid-leaf and basal cells gradual, due to relatively long mid-leaf cells and relatively short basal cells, lamina of basal, sheathing portion of leaf in middle and below with long and narrow cells also along margin; alar cells undifferentiated or a few cells slightly wider than other basal cells and sometimes brownish, unistratose, not or shortly and narrowly decurrent. Perigonia lateral on stem, not or shortly stalked, antheridia protected by oblong-triangular perigonial leaves having obtuse to narrowly acuminate acumen. Inner perichaetial leaves 5.36–7.14 mm long, lower 26–42% oblong and broadly sheathing, above suddenly narrowed to long, narrow acumen. Seta tall, (6–)12–25 mm; capsule obloid, slightly curved, with distinct struma, 0.9–1.4 × 0.5–1.0 mm, 1.3–2.1 times as long as broad, more or less orthogonal; exothecial cells slightly incrassate, mostly slightly collenchymatous; stomata ovate-pored, surrounded by indistinctly radially arranged cells, near base of capsule; peristome orange-red, teeth cleft or perforated to one- or two-thirds down, with longitudinal rows of pits on outside; spores 23–30 µm, very finely rough.

Well-developed O. elongatus has very long leaves, which are narrow above their sheathing base. In oceanic portions of the Scandinavian mountain range and along the Norwegian coast the species often grows in open fens or wet heaths or meadows and then the leaves are mostly spreading and give the plants a very characteristic appearance. This is the kind of plants that made Hagen (1899) distinguish O. wahlenbergii var. elongatus and Hedenäs (2005) raise it to the species level. However, molecular data show that this species is variable both molecularly and morphologically and with the present circumscription, the species includes also plants with different leaf orientations and from different habitats than the plants originally referred to it. Morphologically, this species differs from O. wahlenbergii in that the middle and basal portions of the basal, sheathing lamina have long and narrow cells also along its margin. In Fig. 6. A–D. Oncophorus elongatus A (specimen P251; cf., Table 1). E–G. O. elongatus B (specimen P221, cf. Table 1). A, E. Stem leaves. B, F. Upper leaf acumen. C, G. Marginal and alar portions of sheathing leaf base (margin to the right). D. Portion of leaf at widest point, showing the flat margin.

addition, O. elongatus has longer vegetative leaves than O. wahlenbergii, and some or many leaves have almost always got denticulate or sharply denticulate upper margins, often with denticles on the back of the costa also. Rarely some plants have only a few leaves with denticles along the margin, and their denticles are in addition scattered and obtuse. In such cases the cell pattern of the sheathing lamina can be used to distinguish the two species. As noted by Hedenäs (2005) the spore capsules of O. elongatus mature somewhat before those of O. wahlenbergii.

This species is most frequent in open wetlands and humid forests, where it is found on humus-rich substrates and decomposing wood (Fig. 4). It occurs also on rocks, wet rocks, and on shores. Oncophorus elongatus is the most frequent and widespread member of the genus in Scandinavia (Fig. 3A), and is the only member of the genus that is relatively frequent also in large portions of the southern third of Sweden.