Notes. The type material of Hypnum sipho P. Beauv. consists of five syntypes glued on one small sheet, and another separate syntype in herb Hedwig-Schwägrichen, all in G. At least three taxa are represented, Leptodictyum riparium, Amblystegium varium, and a member of a family other than the Amblystegiaceae. Syntype no. 3 on the small sheet, and the syntype in Hedwig-Schwägrichen, are the only ones consisting of what is nowadays called L. riparium; the one on the small sheet, apparently from Palisot de Beauvois herbarium, is here chosen as the lectotype of Hypnum sipho P. Beauv. A label on the specimen (by Ochyra in 1985) claims that all five syntypes together are the holotype of the name, but this cannot be correct.The type of Amblystegium brevinerve Broth, may at first appear to be a member of Drepanocladus s.str. (cf. Hedenäs, 1993a), but the transition between the alar groups and the laminal cells above is less distinct in A. brevinerve, and the axillary hairs consist of more cells (frequently 3-4 upper cells) than in D. aduncus (1-2(-3) upper cells), to which it is most similar. Leptodictyum species often grow on submerged rocks in rivers, whereas in Drepanocladus only those species with excurrent costae are normally found in this habitat.Leptodictyum riparium has been reported from Mexico, Guatemala, the Bahama archipelago, Cuba, Jamaica, Haiti, Dominican Republic, Venezuela, Peru, and Brazil (e.g., Buck, 1998; Delgadillo et al., 1995; Duarte Bello, 1997; Menzel, 1992; Sharp et al., 1994; Yano, 1981). I have not been able to confirm the reports from Venezuela (Delgadillo et al., 1995) or Peru (Menzel, 1992). On the other hand, Belize, Honduras, El Salvador, and Colombia can be added to the distribution area of the species. The habit of Leptodictyum riparium is more like that of a species of Drepanocladus than of an Amblystegium, where it has sometimes been included. The size (1.6-3.0 mm long stem leaves) immediately sets it apart from all except the largest expressions of some Amblystegium species in the area. In fact, only A. varium commonly gets as large as the smallest specimens of L. riparium. Amblystegium varium can be differentiated from L. riparium by its shorter leaf laminal cells ((15.0-) 17.0-65.0 vs. (34.0-)42.0-l 17.0 µm) and narrower costa (29.5-58.0(-77.5) vs. (45.0-)52.5-l 14.0 µm wide near base). The costa ends ± high up in the acumen in A. varium, rather than 60-75% of the way up the leaf as in L. riparium. Leptodictyum riparium is also frequently confused with Drepanocladus aduncus. However, L. riparium frequently has a complanate foliation, especially in the branches (which does not occur in D. aduncus); the alar cells are more indistinctly delimited from the surrounding cells in L. riparium than in D. aduncus; and L. riparium is autoicous whereas D. aduncus is dioicous. In addition, the upper part of the axillary hairs in L. riparium is 2-7-celled, whereas in D. aduncus it is l-2(-3)-celled. Because axillary hairs of these species are frequent and easy to see when the leaves are removed in the shoot apices, this character is very useful when the other characters mentioned are not sufficient for a certain identification.
Distribution and Ecology: Mexico (303310 m a.s.l.), Guatemala (210-1400 m), Belize (150 m), Honduras (640 m), El Salvador (700-1100 m), Bahama archipelago (altitude unknown), Cuba (450500 m, few specimens with altitude information), Jamaica (150 m), Haiti (1700-1800 m), Dominican Republic (0-230 m), Colombia (2880 m), and Brazil (10-850 m). Also known from farther south in S America. Widespread in temperate N America and Eurasia (reaching subtropical parts); in N, S, and tropical Africa; and in Australia, New Zealand, and Kerguelen. Contrary to most other Amblystegiaceae species found in tropical and subtropical areas, Leptodictyum riparium can be found at both high and relatively low altitudes. It occurs in intermediately mineral-rich to calcareous wet habitats; in swamps, submerged, or on the shores of rivers, springs, dams, or lakes; sometimes in ditches, on rocks, boulders, soil, tree bases, rotten wood, or concrete structures.