Athyrium crassicaule J.P.Roux

Roux, J.P. (2008). Athyrium crassicaule (Woodsiaceae), a new fern species from the Drakensberg, southern Africa. Kew Bulletin 63: 433. https://doi.org/10.1007/s12225-008-9062-6

Type

South Africa, KwaZulu-Natal, Cobham Nature Reserve, Emerald Stream forest, in light shade in forest, near stream, 24 Jan. 2008. J. P. Roux 4478 (holotypus NBG 0210423-1, NBG 0210423-2, NBG 0210423-3, rhizome and complete frond mounted on 3 sheets; isotypus K).

Morphology General Habit

Plants terrestrial-Rhizome erect, sparsely branched from base, central axis to 4 mm in diam., to 90 mm long, closely set with roots and persistent, crowded stipe bases resulting in a structure up to 45 mm in diam., stipe bases somewhat thickened, to 50 mm long and up to 9 mm in diam., castaneous, densely scaled, scales thinly crustaceous, castaneous, linear, twisted, to 14 mm long and 1 mm wide, entire or with a few retrorse marginal outgrowths terminating in an enlarged thin-walled cell, cordate to cordate-imbricate, attenuate towards the apex, terminating in an enlarged thin-walled cell

Morphology Leaves

Fronds caespitose, to 8 per plant, erect to arching, to 1.1 m long; stipe firm, to 47 cm long, proximally castaneous and somewhat thickened, to 9 mm in diam., or up to 6 mm in diam. higher up, yellowish when fresh, drying stramineous, adaxially with a V-shaped sulcus, proximally initially closely scaled, near glabrous later, scales firmly chartaceous, dark brown, margins often slightly paler, linear, attenuate towards the apex, to 14 mm long and 1.4 mm wide, entire; lamina to 59 cm long, to 26 cm wide, lanceolate to narrowly ovate, 2-pinnate-pinnatifid, with up to 21 petiolated pinna-pairs; rachis yellowish when fresh, drying stramineous, sulcate adaxially, sparsely set with scales and minute hairs abaxially, fugacious, scales pale brown, thinly chartaceous, linear-attenuate, to filiform, to 3 × 0.1 mm, entire, twisted, adaxially closely set with unicellular oblong hairs up to 95 µm long, particularly within the sulcus; pinnae near opposite, 1-pinnate-pinnatifid, the basal pinnae widely spaced and reduced in size, distal pinnae more closely spaced, not or hardly overlapping, petiole at lamina base to 2 mm long, gradually reducing in length towards the lamina apex, the small distal pinnae sessile, basal pinnae lanceolate to narrowly elliptic, to 125 × 30 mm, longest pinnae narrowly lanceolate to oblong-attenuate, to 185 × 55 mm, with up to 15 petiolated pinna pairs; pinna-rachis sulcate adaxially, sulcus not confluent with that of the rachis sulcus, stramineous abaxially, sparsely set with scales similar to, but smaller than those on the rachis, narrowly green-winged adaxially, sulcus variously set with unicellular oblong hairs up to 95 µm long, flanked by low interrupted ridges, each terminating in a distal spine; pinnules herbaceous, pale to mid-green adaxially, paler abaxially, near opposite to alternate, pinnatifid, the basal pinnule pairs on the lower 5 to 6 pinna pairs often smaller than the next pair above, the basal pinnule pairs petiolate, petiole to 1 mm long, sessile towards the pinna apex, narrowly ovate, somewhat acroscopically developed, to 21 × 9 mm, glabrous adaxially, or with unicellular oblong hairs up to 95 µm long along the costa, abaxially with few 4 – 7-celled hairs to 0.4 mm long, terminating in an enlarged globose, thin-walled cell, lobes oblong, to 4 × 3 mm, the outer margin acutely dentate, the margins pale, cartilagineous; costa adaxially flanked by low interrupted ridges, each terminate distally in a short or long spine

Morphology Leaves Leaf veins

Venation evident adaxially and abaxially, ending in the teeth near the margin

Morphology Reproductive morphology Sori

Sori up to 9 pairs per pinnule, to 1.2 mm long, mostly along the first acroscopic vein branch of the lobes, larger acroscopic lobes with up to 3 soral pairs; indusium pale brown, chartaceous, lunate, unciform, or hippocrepiform, to 1.4 mm long and 0.8 mm wide, margin lacerate

Morphology Reproductive morphology Spores

Spores brown, rugose, without perispore, 40 – 50 × 28 – 32 µm.

Distribution

Athyrium crassicaule is currently known only from the Drakensberg, occurring from Platberg near Harrismith in the NE Free State Province to Sehlabathebe National Park in Lesotho

Ecology

At Sehlabathebe where the species is frequent, the habitat ranges from streambanks, where it grows with Polystichum sinense H. Christ among Merxmuellera macowanii (Stapf) Conert tussocks, to shaded or partially shaded conditions at the base of Clarens Sandstone boulders and cliffs, away from water. This habitat is subjected to regular vegetation fires, but this appears to have little effect on the plants as rapid regrowth generally takes place after these events. The dense layer of persistent stipe bases clearly acts as a protective layer for the partially subterranean rhizome. The species has also been collected in open forest patches near or away from water, rarely in deep shade; c. 1,500 to 2,378 m

Note

Since the species is more widespread than was initially thought a key to the Athyrium species occurring in Lesotho, South Africa, and Swaziland is provided to aid identification within the region. The robust rhizome of Athyrium crassicaule is the chief distinguishing feature that separates this species from A. newtonii, the only other Athyrium species in the region with an upright rhizome. Although the rhizome itself is relatively thin in A. crassicaule, up to 4 mm in diam., it is closely set with fleshy persistent stipe bases (trophopods) that are up to 50 mm long, resulting in the structure being up to 45 mm in diam. The rhizome is closely branched in the lower parts, resulting in the plants generally forming small crowded clusters. This is in contrast with the unbranched, relatively thin erect rhizome of A. newtonii. The stipe bases are closely set with scales that are significantly longer than those in A. newtonii. In A. newtonii the central axis can be up to 3 mm in diam., but the persistent stipe bases are not as pronounced, or long and thick. The structure rarely exceeds a diameter of 25 mm.