40. MOLENDOA                    Plate 53.

Molendoa Lindb., Utkast Nat. Grupp. Eur. Bladmoss. 29, 1878. Type: Molendoa hornschuchiana (Hook.) Lindb. ex Limpr.

Pleuroweisia Limpr. ex Schlieph., Flora 68: 359, 1885. Type: Pleuroweisia schliephackei Limpr. ex Schlieph.

Ozobryum Smith Merrill, Novon 2: 255, 1992. Type: Molendoa ogalalensis (Smith Merrill) Zand.

Anoectangium subg. Molendoa (Lindb.) Kindb., Eur. N. Amer. Bryin. 2: 317, 1897.

            This genus is found on all continents except Australia and Antarctica, in montane or arctic areas, growing mainly on soil or rock (often calcareous) in wet or seasonally moist places.

            Diagnostic characters are few and somewhat variable. For this reason species of Molendoa are often confused with Anoectangium species, which also are eperistomate and pleurocarpous, and also often have triangular stem sections. Molendoa differs from the latter principally by the presence of a ventral costal stereid band (Pl. 53, f. 6, 22), which, unfortunately, is often absent in Molendoa specimens of small size. Other characters that are found in some but not all species of Molendoa (or which occur only in well-developed populations of certain species), but which are not found in Anoectangium, may be used to refer specimens to the correct genus. These occasional indicator features of Molendoa include glaucous color of the upper leaves, becoming light tan in lower parts of the plant; leaves linear-lanceolate or not keeled; apex rounded, not apiculate; upper margins bistratose (Anoectangium may be bistratose in transverse spaced rows across upper leaf); leaf base much dilated and shoulders sometimes denticulate; superficial cells of the costa quadrate; costa ending before the apex or very broad (up to 7 rows of cells across costa ventrally at midleaf and up to 7 guide cells in the costa); costal transverse section flattened reniform, or showing two stereid bands; laminal cells heterogeneous in shape (Pl. 53, f. 14), or superficial walls (as seen in section) flat and distinctly thicker than the contiguous, anticlinal walls (Pl. 53 6, 22); papillae low, scab-like, crowded; KOH reaction pale yellow (versus yellow-orange); theca macrostomous (Pl. 53, f. 9).

            The leaf shape, leaf section, and propagula are similar to those of Didymodon (sensu Saito 1975a), but Molendoa differs from that genus by the rather distinctive scab-like papillae (in most species) and, of course, the lateral gametoecia. Molendoa clavuligera (not seen) is reported to have clavate leaf apices similar to those of Didymodon johansenii. Molendoa is, on analysis, more closely related to Didymodon than to Anoectangium in some cladograms and is placed in the Hyophileae of the Pottioideae in Cladograms 14–16..

            Pleuroweisia is here treated as a synonym of Molendoa (following the suggestion of Hilpert 1933) in that the key characters of the former are also found in Molendoa. The recognition of the genus Pleuroweisia by several modern authors (Brotherus 1924–25; Hilpert 1933; Chen 1941; Savicz-Ljubiskaja & Smirnova 1970) is probably due to acceptance of technical characters advanced by Limpricht (1890) that in fact have no substance. The calyptrae, alleged (Limpricht 1890; Chen 1941) to cover only the rostrum of the operculum, are also found perched on the rostrum in Molendoa sendtneriana in both microstomous (e.g. Mexico: Müller 1834, MICH, type of Anoectangium glaucescens) and macrostomous (e.g. Mexico: Le Sueur E6a, FH) collections. The type specimen (leaves figured in Pl. 53, f. 23–26 from an isotype, Switzerland, Pontresina, Roseg-Gletschers, Graf, 9-7-1883, H) of Molendoa schliephackei (= Pleuroweisia schliephackei) has calyptrae present only on immature capsules, and, in fact, these partly cover the thecae as well as the opercula. Other characters, such as the recurved leaf margins, rounded apex, rather thick-walled laminal cells, indistinct stem central strand, ovoid perichaetial leaves that sheath the seta, ovoid capsules, and somewhat vesiculose annular cells are also found in various combinations in Molendoa, specifically the highly variable (Pilous 1958; Zander 1977c) M. sendtneriana. The chromosome number of M. schliephackei has been reported (Fritsch 1972) to be the same as that of Molendoa sendtneriana, n = 13. Characters that may prove of significance for M. schliephackei at the species level are the strongly recurved laminal margins and the rather large leaf cells (12–14 µm in diameter), although these are features seen so far only in the type specimen. Other specimens examined that were identified as this species are within the range of variation accepted (Zander 1977c) for M. sendtneriana in the New World, and none match the type of the species in all significant respects. Perhaps Geissler (1985) has a better solution to the problem of variation among these taxa; she viewed M. sendtneriana, M. schliephackei, M. tenuinerve and M. taeniatifolia as synonyms of M. hornschuchiana (as Anoectangium hornschuchianum).

            Previously placed in Anoectangium, Molendoa platyphyllum (Pl. 53, f. 10–15) of the Peruvian Andes and M. warburgii (Pl. 53, f. 16–18) of the United Kingdom are similar in the small plant size, much-branched stems, leaf shape (ovate-triangular with a constricted apex) and costa thin (the former has two stereid bands, but none have yet been detected in the latter). The two differ in papillae shape (the former has low, scattered scabs, while the latter has massive simple or less thickened bifid papillae), but these two species are evidently closely related. Long (1982c) found propagula in the latter species, and he rightly suggested these indicate a closer relationship to Molendoa than to Anoectangium. The mid-North American M. ogalalensis, type of Ozobryum, is similar to these but differs in the lack of a stem sclerodermis, the broader leaf apex, single massive papilla over each bulging lumen, and superficial walls of upper laminal cells not distinctly thicker than the internal walls; this species is distinctive but, in my opinion, not at the generic level. Molendoa ogalalensis is similar in stem section, leaf shape and papillae morphology to Quaesticula navicularis, which differs, however, in the incurved upper leaf margins and terminal perichaetium.

            The Bryotheca E. Levier specimen of Molendoa roylei at NY is Hymenostylium recurvirostrum and other distributed duplicates may also be this species. Hymenostylium characteristically (but not always) lacks a central strand. This and the rectangular, often irregularly thickened median leaf cells are good distinguishing characters for sterile specimens.