Macromitrium altituberculosum E.B.Bartram

Authority

Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)

Family

Orthotrichaceae

Scientific Name

Macromitrium altituberculosum E.B.Bartram

Description

Species Description - Plants slender, dull, olive- to dark-green above, brownish and tomentose below, in irregular, spreading mats. Stems creeping, with numerous, erect branches up to about 1 cm high. Leaves appressed-twisted, sometimes ± spirally appressed-flexuose, the laminae appressed-reflexed and longitudinally folded when dry, wide-spreading, the upper laminae reflexed, the apical portions ofthe laminae forming abaxially positioned pockets when moist, 1.6-2 mm long, keeled below, with a ± broad fold on either side of costa, hngulate to ovate-lingulate, rounded-obtuse, emarginate to mucronate; margins plane, but laminae strongly reflexed, entire except at base; costa excurrent into a short, broad mucro; upper cells 6-8 µm wide, rounded-hexagonal, subquadrate, or rounded, thin-walled to moderately thick-walled, slightly bulging; basal cells rounded-quadrate to rectangular near the costa, becoming longer and narrower near the margin, a few yellowish, enlarged cells on either side of the costa at the insertion, bulging conic-papillose about 1/3 way up leaf, becoming strongly tuberculate (about 12-15 µm high) near the insertion, with a short border of strongly toothed hyaline cells present at the basal margins forming hollow, tuberculate projections up to 25 µm high. Pseudautoicous (dwarf male plants not seen). Perichaetial leaves much shorter than vegetative leaves, 1-1.6 mm long, broadly lingulate, obtuse, mucronate, stiffly erect; basal cells not tuberculate, some cells longer. Setae 3-6 mm long, smooth; capsules 1.2-2 mm long, ovoid-cylindric when mature, becoming ovoid to oblong-ovoid with age, 8-ribbed; annulus of 2-3 rows of thin-walled, subquadrate cells; exothecial cells irregularly quadrate-rounded to rectangular-elliptic, often about 2:1, thick-walled, ± differentiated along the ribs; stomata numerous, in the neck and at the base ofthe urn, well-developed; exostome teeth 16, erect-inclined when mature, recurved when old and dry, finely papillose-striate, the outer layer of plates thick; endostome segments 16, not quite as long as the exostome, erect, hyahne, coarsely papillose, of 1 to 2 rows of cells, with a basal membrane 1-3 cells high. Spores anisosporous, 13-20(-23-)25-37 µm. Calyptrae naked, smooth, deeply laciniate.

Discussion

Fig. 478

M. altitubercuhsumBartt. ex Grout, Bryologist 47: 17. 1944.

No other species in the genus has such broad leaves, and the lingulate-ovate leaves with rounded-obtuse and emarginate to mucronate apices distinguish this from all other Mexican Macromitria. It is the only Mexican species to have endostome segments not fused into a membrane. The very large tubercles at the basal margins of the leaf are also distinctive.

Superficially, the gametophytes of M. altituberculosum are similar to those of Groutiella tumidula, which is easily differentiated by basal leaf cell and sporophyte characters. However, the similarity in leaf shape and set provides a remarkable case of parallel evolution. Groutiella tumidula grows in lowland forests, whereas the Macromitrium appears to be montane.

Macromitrium altituberculosum is closely related to M. stellulatum (Hornsch.) Brid., and more collections m ay show them in intergradation. The type of M . stellulatum (NY!) has fewer tubercles at the leaf base and lacks the large basal marginal tubercles. For now, I choose to treat them as distinct.

Distribution

The type specimen was collected on rock (in Guatemala), but subsequent collections came from tree trunks in montane forests; known from three collections in Chiapas, one near the Oaxaca border.—Southern Mexico; northern Guatemala.

Guatemala Central America| Mexico North America|