Macrocoma tenue subsp. sullivantii (Müll.Hal.) Vitt

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

Macrocoma tenue subsp. sullivantii (Müll.Hal.) Vitt

Description

Species Description - Plants slender, in brown to olive-green, sometimes dense mats, the younger portions often light-green. Stems creeping, irregularly branched, usually with numerous erect-ascending or sometimes horizontal branches up to 1 cm long, these often with short branchlets. Leaves erect-appressed when dry, spreading to wide-spreading when moist, keeled, particularly below, 0.7-1.3 mm long, lanceolate to ovate-lanceolate, sharply acute, occasionally broadly acuminate and very rarely narrowly obtuse in older leaves; margins plane and entire above, reflexed and rough below because of bulging cells; costa prominent, ending just below the apex, sometimes producing rhizoids at back; upper cells (5—)6—10(—13) µm wide, thick-walled, larger near the costa, with marginal cells usually smaller (about 5-7 µm wide), rounded-quadrate, smooth; cells just below the apex flat, gradually becoming bulging at midleaf or just above; basal cells strongly bulging to bulging-papillose, rounded to elliptic at margins, grading to elliptic or rectangular and sometimes ± nodose at the costa up to 22 µm long. Gonioautoicous. Perichaetial leaves longer, slenderly acute; lower cells longer; paraphyses numerous, persistent around the base ofthe seta. Setae (2.5-)4-6.5(-8) mm long; capsules 1.3-2.4 mm long, exserted, oblong-cylindric to fusiform when mature, ovoid-fusiform and often ± lightly ribbed in the upper portion when old, the upper 1/3 sometimes puckered; exothecial cells not or slightly differentiated, rounded to rounded-oblong, up to 27 µm long, thickwalled; stomata superficial, in the neck and lower portion of the urn; peristome consisting of 2 coarsely papillose or smooth, pale-yellowish to whitish membranes a few cells high. Spores (20-)25 x 42(-50) µm wide, finely papillose. Calyptrae hairy, obscurely plicate, dark-yellow, mitrate but often splitting along 1 rib.

Discussion

Fig. 486

M. tenue (Hook. & Grev.) Vitt ssp. sullivantii (C. Müll.) Vitt, Bryologist 83: 413. 1980.

Macromitrium sullivantii C. Mull., Bot. Zeitung 20: 361. 1862.

M. paraphysatum Mitt., J. Linn. Soc, Bot. 12: 198. 1869.

M. braunioides Card., Rev. Bryol. 36: 108. 1909.

Macrocoma sullivantii (C. Müll.) Grout, Bryologist 47: 5. 1944.

Macrocoma tenue ssp. sullivantii, by far the most common member of the genus in Mexico, is distinguished by its peristome reduced to two coarsely papillose membranes each a few cells high. The areolation is distinctive: The lower cells are strongly bulging to bulging-papillose and often give the lower leaf margins a crenulate appearance. The cells gradually become less bulging above and at midleaf are generally slightly bulging. In the upper portion, the cells near the costa are most often slightly bulging and rounded-elliptic, thick-walled, and relatively large (6-10 µm wide). They usually become gradually smaller (5-7 µm), less bulging or occasionally flat, and more quadrate at the upper margins. In well-developed specimens some upper cells tend to be longer than wide (2-3:1); however, leaves with uniformly rounded cells occur on the same plants, and these longer-celled leaves are often found in association with perichaetia. In a few Mexican specimens the upper cells tend to be flat; in others they are bulging, and a few may have papillae. Such variation falls within an allowable range for a widely distributed species.

A well-developed peristome segregating M. frigidum and M. orthotrichoides from M. tenue ssp. sullivantii can usually be detected in immature capsules. When sterile, M. frigidum is easily distinguished by broad leaves and strongly bulging upper leaf cells. Macrocoma orthotrichoides cannot always be told with certainty from M. tenue ssp. sullivantii, but in M. orthotrichoides the leaves tend to be less ovate, the upper cells are often uniform-sized and flat, and the calyptrae are sparsely hairy. In M. tenue ssp. sullivantii, the leaves are sometimes ovate-lanceolate, the upper cells are often bulging and larger near the costa but smaller and flatter at the margins, and the calyptrae are usually quite hairy.

Misuse of the name Macrocoma hymenostomum (Mont.) Grout was discussed by Vitt (1973a). The name should be excluded from the Mexican flora; Mexican collections can generally be referred to M. tenue ssp. sullivantii.

Distribution

On trunks and branches of trees in dry, open forests; Chiapas, Coahuila, Durango, Hidalgo, Michoacan, Nuevo Leon, Oaxaca, Puebla, San Luis Potosi, Tamaulipas, Veracruz.—Mexico; Central America to Argentina and Chile; Southern Appalachian Mountains (Georgia and North Carolina); Hawaii; eastern Asia; Japan.

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