Bonjean's Dicranum Moss

Dicranum bonjeanii was recorded from Maine by B. H. Allen (1998b). It is difficult to distinguish from the myriad forms of the polymorphic D. scoparium. Indeed, few of the many herbarium collections from North America named D. bonjeanii are actually that species or at least what is known as that species. It has been noted before (R. R. Ireland 1982) that it may be merely an enviromental form growing in a calcareous, often hydric habitat. Most Europeans (e.g., A. J. E. Smith 1978; E. Nyholm 1986+, fasc. 1) recognize the species as it occurs in Europe, and some that come to North America to collect (e.g., R. K. Tuomikoski et al. 1973) find the species to be distinct on this continent. However, H. A. Crum and L. E. Anderson (1981) and other North American bryologists have synonymized the species with D. scoparium. D. Briggs (1965), who cultivated and studied British plants of both D. bonjeanii and D. scoparium under controlled environmental conditions, found that while they show wide intraspecific variation, especially in regard to the leaf habit and undulation, and thought that they should be kept as separate taxa because each maintains a distinctive array of gametophytic characters. Also, both species are distinctive ecologically: D. bonjeanii prefers eutrophic fens, whereas D. scoparium usually grows in decidedly dry to mesic woodlands, on soil, humus, humus over rock, stumps and logs, tree bases, etc.

Dicranum bonjeanii is best known by its glossy, mostly erect, nearly straight, undulate leaves with broadly acute apices, weakly developed marginal teeth and, what is most important, two poorly developed ridges present only near the leaf apex on the abaxial surface of the costa. The two ridges on the costa, best seen in cross section, will distinguish the species most of the time from D. scoparium which usually has four ridges on its costae. Its preference for eutrophic fens and other calcareous habitats, while avoiding acid substrates, is important from an ecological standpoint and helps give a clue to the identity of the species.

Plants medium-sized to large, up to 6 cm high, dull pale green or brownish green, shiny, in dense tufts. Stems erect, simple or branched, radiculose at base. Leaves in many rows, not homomallous, somewhat crispate when dry, erect-patent when moist, lance-lingulate, gradually narrowed down and slightly undulate from the upper third, obtuse at the apex; margins plane, entire below, irregularly serrate near the apex; costa thin, narrow, subpercurrent, serrate or roughened at back in the upper part; upper cells rounded short-rectangular to rhomboidal; basal cells rectangular, thick-walled, somewhat porose, forming several rows of narrower cells at the margins; alar cells quadrate to short-rectangular, thick-walled, somewhat inflated, not extending to the costa. Dioicous. Male plants dwarfed. Setae single or in cluster of 2, slender, up to 3.5 cm long, light brownish to reddish; capsules cylindric, inclined to horizontal, curved, sometimes strumose at base, plicate when dry; opercula long-rostrate, as long as the urns; annuli in 1–2 rows of large cells; peristome teeth dicranoid. Spores brownish, papillose.

Plants in loose tufts, yellow to yellowish green, glossy. Stems 2-8 cm, scarcely tomentose with whitish to reddish brown rhizoids. Leaves erect-spreading, sometimes nearly appressed, flexuose, little changed when dry, undulate or rugose, (3.5-)4-5.5(-6) × 1-1.5 mm, flat to ± concave proximally, subtubulose above, from a lanceolate base to a short, broadly acute apex, distal part of stem often with ovate, short-subulate, blunt leaves; margins serrate in the distal half; laminae 1-stratose; costa ending just before the apex, sometimes with two poorly developed toothed ridges above on abaxial surface, ¹/13-¹/8 the width of the leaves at base, row of guide cells, two thin stereid bands, adaxial epidermal layer of cells not differentiated, the abaxial layer with a few (usually 2) cells differentiated in distal part of the leaves; cell walls between lamina cells not bulging; leaf cells smooth; alar cells 2-stratose, well-differentiated, sometimes extending to costa; proximal laminal cells long, sinuose, pitted, (28-)47-71(-113) × (5-)9-11(-14) µm; distal laminal cells short-linear, sinuose, pitted, (25-)36-51(-73) × (5-)8-14(-20) µm. Sexual condition pseudomonoicous; dwarf males on rhizoids of female plants; interior perichaetial leaves abruptly long-acuminate, convolute-sheathing. Seta 2.5-3.5 cm, solitary, rarely two per perichaetium, yellowish brown to reddish brown. Capsule 2.5-3 mm, arcuate, inclined to horizontal, striate when dry, yellow-brown; operculum 1.7-3 mm. Spores 14-28 µm.

Distribution: China, Russia, Europe, and North America.

Habitat: on damp soil or rocks.

Type. Italy.

Dicranum bonjeanii De-Not.; Lisa, Elenco 29. 1837
Dicranum palustre B.S.G. Bryol. Eur. (37-40:) Dicranum 39. 1847.
?Dicranum dipteroneuron C. Mull. Flora 70; 221. 1887.
Dicranum leioneuron Kindb.; Macoun, Bull. Torrey Club 16: 92. 1889.
Dicranum congestiforme C. Mull. & Kindb.; Macoun, Cat. Can. PI. 6: 29. 1892.
Dicranum plano-alare C. Mull. & Kindb.; Macoun, Cat. Can. PI. 6: 31. 1892.
Dicranum undulifolium C. Mull. & Kindb.; Macoun, Cat. Can. PI. 6: 32. 1892.
Dicranum subpalustre C. Mull. & Kindb.; Macoun, Cat. Can. PL 6: 33. 1892.
Dicranum Roellii Kindb.; Roll, Hedwigia 35: 60. 1896.
Dicranum hyalinum Kindb.; Roll, Hedwigia 35: 61. 1896.
Dicranum perichaetiale Kindb.; Roll, Hedwigia 35: 61. 1896.
Dicranum alatum Card. & Ther. Bot. Gaz. 37: 364. 1904.
Dioicous: male plants minute on tomentum or large and in more or less separate tufts: fertile plants in extensive, mostly dull-green or pale, yellowish-green tufts, with tomentose stems up to 15 cm. high: leaves erect or spreading-flexuous, undulate or smooth, usually not curved.■secund, mostly 6-8 mm. long and 1-1.5 mm. wide, lanceolate, gradually narrowed to a broadish obtuse or acute, serrate to entire point more or less grooved but usually scarcely tubulose; costa vanishing below the apex, from serrate-winged to nearly smooth on the back, in crosssection as in D. scoparium; leaf -cells more or less thickened pitted and elongate throughout, the rr edian ones about 12 fi wide and 25-50 fx long or sometimes not more than one and one half times as long as wide, the alar forming a reddish-brown or more or less hyaline cluster extending .about half way to the costa: sporophyte as in D. scoparium.
Type locality: Italy.
Distribution: Labrador to Alaska and southward to Virginia, Ohio, and Colorado; also in