Macromitrium xenizon B.H.Allen & W.R.Buck
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Authority
Buck, William R. 2003. Guide to the plants of central french Guiana. Part 3. Mosses. Mem. New York Bot. Gard. 76: 1-167.
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Family
Orthotrichaceae
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Scientific Name
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Type
Typus: French Guiana. Canton de Maripasoula: Commui de Saul, along trail to Pic Matecho, near km 2, between the Rou de Belizon near Crique Saint-Eloi and camp at km 6.5 on Crique Saint-Eloi, 3°43'34"N, 53°13'23"W, ca. 200 m; fallen canoj branches in primary moist forest, 23 September 2000, William J Buck 38090 (holotype, NY).
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Description
Latin Diagnosis - A congeneris localibus foliis aliquando fragilibus, folii margii basali praebens dentes tumidos, folii cellulis basalibus tuberculai differt.
Species Description - Plants small to medium-sized, branches dull green from a reddi: tomentose creeping stem, stems to 5 cm long, branches 2-4 mm Ion Leaves weakly spiraled and contorted or inrolled above when dry, ovate-lanceolate to lanceolate, acute to broadly acute, (1.5)2-2.8 x 0.5-0.75 mm, usually fragile and breaking irregularly near midleaf: margins entire above, with swollen teeth near leaf base, plane: costa subpercurrent; cells rounded-hexagonal, 8-10 µm in diameter, mammillose, somewhat longer below; inner basal cells short-rectangular, ca. 6 x 12 µm, thick-walled, tuberculate. marginal basal cells rectangular in 8-12 rows, thick-walled, porose, extending well less than 1/4 the leaf length. Perichaetial leaves not strongly differentiated. Setae 9-11 mm long, red, smooth; capsules 2-2.2 mm long, ovoid, smooth, or weakly furrowed at neck: opercula not seen; intact peristome not seen, short membrane present. Spores anisosporous, 18-22 µm and 24-28 µm, papillose. Calyptrae not seen.
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Discussion
The epithet was found as a way in which to have both an x and a z in the same word. It is derived from the Greek ^eut^cov, meaning astounding. The distinguishing features of Macromitrium xenizon are its fragile, mostly broadly acute leaves with subpercurrent costae; rounded-hexagonal, mammillose upper leaf cells; weakly differentiated basal leaf cells; and swollen teeth at the basal margins. The swollen basal marginal teeth of M. xenizon are an especially distinctive feature of this species. This feature is found sporadically within Macromitrium and also occurs in Groutiella and Cardotiella. The basal marginal teeth are best developed on short leaf decurrencies and they are most clearly seen on leaves still attached to the stems. Macromitrium punctatum is similar to M. xenizon in size, overall leaf shape, and general leaf areolation. It differs from M. xenizon in having acute to shortly acuminate leaves with percurrent to short excurrent costae, basal tubercula either absent or very weakly developed, and entire basal margins. Florschiitz (1964) first called attention to this species, but rather than describe it as new, he referred it to M. portoricense. Macromitrium portoricense, here synonymized with M. podocarpi, is similar to M.xenzion in having a subpercurrent costae and enlarged, swollen teeth on the basal leaf margins. this species, however, has smaller plants (leaves mostly less than 2mm long, setae 4-6mm long, capsules 1-1.5 mm long) than M. xenizon with distinctly creeping stems; non fragile, tightly crispate leaves; and more strongly differentiated basal leaf cells (i.e., long-rectangular, incrassate, porose, and strongly tuberculate). Additional specimens have been seen from Surinam (Allen 19265A, BBS, MO; Florschiitz & Florschiitz 395,1320, U), French Guiana (Montfoort & Ek 675, U), and Guyana (Jansen-Jacobs et al. 2455, U, c.fr.).
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Distribution
In non-flooded moist forests, rare, ca. 200 m, on tree branches in the canopy.
French Guiana South America|