Monographs Details: Metzgeria bartlettii Kuwah.
Description:Latin Diagnosis - Frons ca. 1.5 cm longa, alae 8-18 cellulis latae, costa dorsali setosa, cellulis epidermalibus dorsalibus 2-5(-6)-, ventralibus 2-6-seriatis; cellulae alares medianae 19-30(-37) x 17-26(-30) µm. Gemmae marginales, valde concavae; dioica.
Species Description - Thallus small, ca. 1.5 cm long, 0.3-0.7 mm wide, obtuse at apices, convex, pale yellowish green when dried, adventitious shoots commonly produced. Dorsal epidermal cells of midrib arranged in 2-5(-6) rows, 19-48 x 14-26(-30) µm, cell walls thickened; ventral epidermal cells of midrib in 2-6 rows, 22-56 x 14-33 µm, cell walls somewhat thickened. Lamina 8-18 cells wide from midrib to thallus margin, with laminal cells small, somewhat thick walled, trigones small. 19-30(-37) x 17-26(-30) µm in middle, 19-48 x 15-24(-30) µm at thallus margin; thick, smooth and pellucid structure developed chieffy on dorsal surface of lamina; thallus cells pellucid. Thallus margin hirsute, hairs often short, 44-104 µm long, geminate or single, also hirsute on dorsal and ventral surfaces of midrib, very short on dorsal surface, 20-59 µm long, all hairs straight, bristle-like. In transverse section midrib 60-104 µm thick, arched on both dorsal and ventral sides, epidermal cells 6.7-15 µm thick on both sides, distinct or little distinct from medulla consisting of 10(-11) cells in three tiers, 7.4-24(-30) x 5-15 µm, thick-walled, with laminal cells 7.4-15 µm thick in mid-lamina. Gemmae at thallus margin, very weakly attached, strongly concave, to 25 cells long while still attached to thallus, hirsute at margins, hairs short, straight. Dioicous. Male branches globose to subglobose, 250-330 × 180-290 µm in diameter, without hairs, midrib epidermal cells (26-)41-74 x 3.7-7.4(-19) µm, laminal cells relatively large, 24-44 × 19-28 µm; midrib often indistinct, with epidermal cells often in one row partly. Female involucres broadly obovate with a deep apical notch, 250-400 µm long, hirsute at margins and outer surface, with straight, needle-like hairs, constituent cells 19-37 x 17-30 µm. Sporophyte not known.
Metzgeria bartlettii is unique in the Metzgeriaceae by having hairs on the dorsal surface of thallus which are strictly limited to the midrib. This peculiar distribution of hairs at once separates the species from all other taxa ofthe family. In Apometzgeria, and in sect. Hirsuta of Metzgeria where the dorsal surface of thallus is very hirsute, hairs are produced on the whole surface. The distribution and form of hairs are of great taxonomic importance in the family (Kuwahara, 1978, 1984, 1986).
The chief characteristics of Metzgeria bartlettii, which may be placed temporarily in sect. Multiseria, are: (1) on the dorsal surface only midrib hirsute; hairs short, bristle-like, (2) dorsal epidermal cells of the midrib in 2-5(-6) rows, ventral epidermal cells in 2-6 rows, (3) lamina 8-18 cells wide, (4) laminal cells small, 19-30 (-37) × 17-26(-30) µm in the middle, (5) a thick, smooth, pellucid, cuticle-like structure distinct chiefly on dorsal surface of the lamina, (6) gemmae produced at the thallus margin, strongly concave, and (7) in transverse section the medulla of the midrib consisting almost entirely of 10 cells in 3 tiers.
The type specimen, Bartlett 21299: 45/b, bears abundant female organs and gemmae, but no male organs; most gemmae were observed in the free condition. Bartlett 2I298: 63/c contains abundant male organs, but only some female organs.