Heteroscyphus assurgentissimus J.J.Engel, Thouvenot & Frank Müll.

Thouvenot, Louis, 2023, A taxonomic revision of the Lophocoleaceae Vanden Berghen (Marchantiophyta) of New Caledonia, Cryptogamie, Bryologie 20 (1), pp. 1-60 : 14-15

Heteroscyphus assurgentissimus J.J.Engel, Thouvenot & Frank Müll.

( Fig. 6 )

Nova Hedwigia 113: 67 ( Engel et al. 2021).

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Type: New Caledonia. South Province, Parc Provincial de la Rivière Bleue , c. 200- 380 m, lowland rain forest, on a rockface, 5.IX.2001, Müller NC327 (holo-, DR; iso-, F, hb. Thouvenot) .

DISTRIBUTION IN NEW CALEDONIA. — Only known from the type locality in South Province.

TOTAL RANGE. — Endemic.

DESCRIPTION

Further description and illustrations in Engel et al. (2021). Dioecious.

Habit

Plants rigid, up to 5 mm wide when flattened, the shoot tips sharply dorsally assurgent; ventral-intercalary branching frequent; stems narrow for plant size, 0.20-0.30 mm wide; leaves subopposite, stiffly dorsally assurgent, often forming a gentle bow-like arch, the adaxial face of opposing leaves facing one another and forming a deep narrow channel; leaves closely imbricate, dorsally connate and forming an elevated, laminar lip to c. 4 cells wide; leaves moderately convex in dorsal sector, moderately abaxially concave in ventral sector.

Leaves

1.50-2.50 mm long, 0.90-1.30 mm wide at widest point, elongate ovate-trapezoid to lingulate, distinctly narrowed toward the apex, moderately to distinctly dilated in ventral-basal sector; apex bifid to 0.05-0.10, the lobes divergent, occasionally parallel, the ventral lobe often larger than the dorsal, the dorsal lobe at times reduced to a small tooth or lacking, the lobes narrowly acute to acuminate, the sinus mostly lunate, occasionally narrowly rounded; lamina margins entire.

Cells

30-47 µm wide, 37-57 µm long, somewhat larger near leaf bases, median leaf cells with strong secondary thickenings of the radial walls, each thickening interrupted by a single, large, clearly defined pit, the wall thickenings converging at the cell junctures to form massive nodose trigones.

Underleaves

2.3-3.5 times the stem width when flattened, connate with the leaves on both sides, connate portion 3-6 cells wide, imbricate, stoutly ovate to subreniform, 0.80-1.30 mm long, 0.80-1.10 mm wide; apex 2-4-lobed, the median pair of lobes often larger, the lobes ± parallel, acute-apiculate to acuminate, entire or with a tooth toward the outer margin, lamina margin on each side with 1-5 small teeth.

Gametangia

Gynoecia not seen; androecia small for plant size, hidden by leaves in dorsal aspect, on abbreviated, determinate, ventralintercalary branches, the androecia foliose, with 2-5 pairs of bracts, the bracts strongly dorsally assurgent, suberect, similar to leaves in shape and form except the bracts are more concave and the apex is notably more narrowed, the apex bidented, the base concave ventricose, the dorsal pocket more strongly inflated, with a several-celled tooth distally; the antheridia stalk biseriate; bracteole stoutly ovale, bifid to c. 0.5, the lamina margins each with a small tooth.

COMMENTS

Heteroscyphus assurgentissimus clearly stands out by: 1) dorsally assurgent leaves and shoot apices; 2) strictly ventral-intercalary branching; 3) ovate trapezoid to lingulate, bifid leaves; and 4) massive trigones extending into strongly thickened cell walls narrowly pitted. It could be regarded as close to Cryptolophocolea explanata by the leaf and underleaf shapes, but the latter species can be easily separated from H. assurgentissimus by its complanate habit, thin-walled cells without trigones and gametangia on elongate shoots.

Figures

FIG. 6. — Heteroscyphus assurgentissimus J.J.Engel, Thouvenot & Frank Müll.: A-D, leaves; E, shoot habit in dry condition, lateral view; F-H, K, L, underleaves; I, shoot portion, ventral view; J, leaf cells. All illustrated from the holotype. Scale bars: A-D, F-H, K, L, 500 µm; E, I, 1 mm; J, 20 µm.