Monographs Details: Metzgeria crassipaginula Kuwah.
Authority: Buck, William R. 1987. Bryostephane Steereana: A Collection of Bryological Papers Presented to William Campbell Steere On The Occasion of His 80th Birthday. Mem. New York Bot. Gard. 45: 1-749.
Family:Metzgeriaceae
Description:Latin Diagnosis - Frons ca. 1 cm longa, paginula crassissima; alae 7-11 cellulis latae; pili rectiformes, marginales solitarii; costae cellulae epidermales dorsales 2-, ventrales 2(-3)-seriatae; costa transversahter e 10-14 cellulis meduUosis valde crassis constans; dioica.

Species Description - Thallus small, slender, ca. 1 cm long, 0.29-0.58 mm wide, obtuse at apices, somewhat convex, pale yellowish green when dried, adventitious shoots common. Dorsal epidermal cells of midrib arranged in 2 rows, 44-100 x 20-30 µm, slightly thick-walled, ventral epidermal cells of midrib in 2(-3) rows, 24-63 x 30-48 µm, moderately thick walled. Lamina 7-11 cells wide from midrib to thallus margin, with laminal cells 25-59 × 22-37 µm in middle, cell walls somewhat thickened, with small trigones, cells at margin typically narrow and often elongated, 22-74 x 11-22 µm; thallus cells pellucid, with very thick, smooth and pellucid structure developed on dorsal surface and margin of thallus. Male thallus often smaller, with lamina 4-11 cells wide. Hirsute at thallus margin and on ventral surface of midrib, hairs straight, typically long and needlelike, 70-190 µm long, hairs at thallus margin borne singly from underside of marginal cells. In transverse section midrib 60-81 µm thick, weakly arched on dorsal side and weakly or strongly arched on ventral side, dorsal epidermal cells thin, 4-9(-15) µm thick, ventral epidermal cells sometimes weakly triangular, 7.4-16 µm thick, medulla consisting of 10-14 cells in 3-4 tiers, 7.4-16 × 3.7-11(-15) µm, very thick walled, with laminal cells 7.4-15(-22) µm thick in mid-lamina. Gemmae not seen. Dioicous. Male branches globose to subglobose, 150-270 µm in diameter, without hairs, epidermal cells of midrib 41-74 x 5.6-11 µm, laminal cells 26-63 x 22-33 µm. Female involucres obovate with an apical notch, 170-240 µm long, ca. 12 cells long, hirsute on outer surface and margin, hairs straight, constituent cells 20-48 × 15-28 µm. Calyptra cyUndrical, 1-1.6 mm long, hirsute on outer surface, hairs straight. Capsule valves 440-740 µm long, 190-240 µm wide in middle. O n outer layer of capsule wall semicircular thickenings distinct, along valve margin tangential bands of thickening present, without or with very weak semicircular thickenings, cells 26-48 X 7-22 µm; on inner layer radial wall moderately thickened with local nodulose thickenings, complete or incomplete semiannular bands of thickening on tangential wall common, cells 33-67 x 7-16 µm. Elaters 190-320 µm long, 3.7-7.4 µm wide in middle; spores reddish brown, 15-18.5 µm in diameter, with granular surface.

Discussion:

Figs. 17-31.

Type: NEW ZEALAND. North Island: Kaimai Range, alt. 860 m, epiphyllous on the leaves of Coprosma lucida, 4 Jul 1977, J. K. Bartlett 21297: 4/c (holotype welt H8725; isotypes JE, NY).

The extraordinarily thick, smooth, pellucid, cuticle-like structure developed on the dorsal surface ofthe thallus in Metzgeria crassipaginula is unique. N o similar structure is known in the Metzgeriaceae, except in M . bartlettii described in the preceding section of this paper. In M . bartlettii, however, that structure is not as thick as in M. crassipaginula and is chieffy present on the dorsal surface ofthe lamina, while it is produced over the whole dorsal surface of the thallus, including the midrib and thallus margin, in the present species.

In transverse section of the thallus of Metzgeria crassipaginula, the cuticle-like structure is often nearly as thick as the lumina ofthe laminal cells, and normally thicker than the lumina of the dorsal epidermal cells of the midrib. In surface view, the very thick, more or less light-reflecting condition of the cuticle-like structure of the thallus margin is very distinctive and readily distinguishes this species from all other members of the Metzgeriaceae. N o special ecological conditions were noted with the three specimens of M. crassipaginula and M . bartlettii which might have caused the production of such a remarkable structure.

The main characteristics of Metzgeria crassipaginula, which belongs to sect. Biseria, subsect. Biseria (Kuwahara, 1984), include: (1) an extraordinarily thick, smooth, pellucid cuticle-like structure on the dorsal surface of the thallus, (2) dorsal epidermal cells of the midrib in two rows and ventral epidermal cells also in two rows but often partly in three rows, (3) lamina 7-11 cells wide which in the male is often smaller (4-11 cells wide), (4) laminal cells moderate in size, 25-59 × 22-37 µm in the middle, (5) thallus margin bordered by a very thick cuticle-like structure and by a row of narrow, often elongated marginal cells, (6) hairs straight, typically long and needle-like, at the thallus margin originating singly from the underside of the marginal cells, (7) in transverse section the medulla of the midrib consisting of 10-14 very thick walled cells in 3-4 tiers and (8) spores 15-18.5 µm in diameter.