Flora of New Zealand Series

Diplophyllum (Dumort.) Dumort., Recueil Observ. Jungerm. 15. 1835; nom. cons.

Jungermannia sect. Diplophyllum Dumort., Syll. Jungerm. Europ. 44. 1831.

Type (cons.): Diplophyllum albicans (L.) Dumort. (≡Jungermannia albicans L.)

Plants prostrate or erect, often in thin, flat patches, clear green or yellowish green (in shade) to yellowish brown, or reddish to reddish orange to reddish brown to blackish, small to medium-sized, to 4.5 mm wide. Branching sparing, the branches lateral-intercalary (rarely displaced to ventral angle of leaf); ventral-intercalary branches present in Diplophyllum recurvifolium. Stem with cortex in 1–2 layers (3–5 in D. albicans and subg. Macrodiplophyllum), of ± firm-walled cells; medullary cells larger, often mycorrhizal with age. Rhizoids scattered. Leaves usually lying in one plane, complicate bilobed, the two lobes usually widely divergent, at least ventral halves widely spreading (sometimes squarrose), the keel rounded or obtuse, never winged, the base ± sheathing. Ventral lobe narrowly lingulate, ± falcate, typically more than 2× longer than wide, distinctly decurrent at the base ( subg. Macrodiplophyllum) or not decurrent. Dorsal lobe similar to the ventral but smaller and shorter (subequal to the ventral in subg. Austrodiplophyllum), mostly suberect or obliquely spreading (except D. verrucosum). Leaf lobes with apices rounded or blunt to apiculate (long-acuminate in D. andicolum), the apices and margins denticulate or serrulate by small, sharp teeth. Cells small, usually firm-walled, the median cells with trigones small or inconspicuous (except subg. Macrodiplophyllum); marginal cells in several rows, often strongly and equally thick-walled, isodiametric; basal cells of ventral lobe and keelar region elongate-rectangular (ca. 3–5× longer than wide and often forming a sharply delimited vitta); surface of median cells with dense, often large papillae, the papillae often inconspicuous or absent in marginal cells. Oil-bodies (Schuster, 1974a) distinctly segmented, papillose, usually 2–4(5) per intramarginal cell, 10–16 per elongated cell of basal, keelar region. Gemmae quadrate to polygonal-stellate, 1–2-celled (to 3–4-celled in subg. Macrodiplophyllum), with strongly thickened angles.

Dioecious, autoecious or paroecious. Androecial bracts leaf-like but with bases ventricose; antheridial stalks long, uniseriate or variably l–2(3–4)-seriate. Gynoecial bracts leaf-like but ± larger, sheathing perianth at base only. Perianth weakly to moderately dorsiventrally compressed, especially above, elliptical in section below, distally deeply plicate, somewhat narrowed to the mouth, the mouth dentate to laciniate.

Capsule ellipsoidal, the wall 3–4-stratose; outer layer of cells with one-phase development, with nodular to spur-like thickenings (Diplophyllum domesticum) or at times locally with a suggestion of a two-phase development: longitudinal walls with pigmented thickenings few or absent alternating with those with strong nodular to spur-like thickenings; inner layer of cells with nodular to often spur-like thickenings that occasionally tangentially extend to form incomplete to (less often) complete semiannular bands.

Spores 9–15 µm in diam., irregularly and finely papillose-vermiculate, the markings at times in part anastomose to form elevated, weak tubercles at the intersections, the spores at times with distinct, sharply defined, broad vermiculate markings. Elaters tortuous, 6–8 µm, bispiral.

Diplophyllum is the second largest genus in the family, with 27 species worldwide, but has a greater representation in Austral areas than the largest genus, Scapania. Engel and Merrill (1998) recognized three subgenera, and of these, two occur in Austral areas.

1) subg. Austrodiplophyllum R.M.Schust. has four species, all Austral in distribution; D. squarrosum Steph. (Engel and Merrill, 1998; Grolle, 1965d) and D. recurvifolium C.Massal. (Massalongo, 1928; Engel and Merrill, 1998; Schuster, 1971b, 2002a) occur in southern South America. Diplophyllum verrucosum R.M.Schust. (Engel and Merrill, 1998; Schuster, 1968a, 2002a) and D. gemmiparum J.J.Engel & Merrill (Engel and Merrill, 1998) occur in our area.

2) subg. Macrodiplophyllum Buch has three species and is North Pacific; see Engel and Merrill (1998) for distribution of the species.

3)  subg. Diplophyllum has nine Austral species. Interestingly, only one species, D. acutilobum Steph., occurs in southern South America (Engel, 1978) and the Falkland Islands (Engel, 1990a), contrasted to six species in Australasia. Of these, D. novum J.J.Engel & Merrill is endemic to New Zealand, D. dioicum R.M.Schust. occurs in New Zealand and Tasmania, D. domesticum (Gottsche) Steph. occurs in New Zealand, Tasmania, Victoria and New South Wales, and D. androgynum J.J.Engel & Merril l, D. angustifolium J.J.Engel & Merrill and D. incrassatum J.J.Engel & Merrill are endemic to Tasmania (see Engel and Merrill, 1998). Diplophyllum marionense S.W.Arnell is endemic to Marion Island (Arnell, 1953) [=D. acutifolium fide Arnell (1956, p. 529). “ D. randii S. Arnel l,” mentioned by Schuster (1963b, p. 272) from Marion Island, was not listed by Grolle (1971a)]. Diplophyllum africanum S.W.Arnell occurs in Kenya (Mts. Elgon and Kilimanjaro, 3400–4200 m) (Arnell, 1956), Rwanda (Mt. Elgon and Kilimanjaro, 3650 m) (Váňa et al., 1979), and Tanzania (Bizot and Pócs, 1974).

Schuster (1974a, 2002a) included a fourth subgenus, subg. Protodiplophyllum R.M.Schust. (type =Diplophyllum obtusifolium (Hook.) Dumort.) and included 11 Austral and four Laurasian species (Schuster, 2002a). We would include this subgenus in the synonymy of  subg. Diplophyllum.