70. STONEA Plate 101.

Stonea Zand., Phytologia 65: 431, 1989. Type: Stonea oleaginosa (Stone) Zand.

Plants gregarious, mostly buried in soil, green above, reddish brown below. Stems seldom branching, very short, to 0.3 µm in length, transverse section rounded, central strand absent, sclerodermis absent, hyalodermis absent; axillary hairs 2–4 cells in length, basal cells firm-walled; lower stem clothed with fine rhizoids. Leaves incurved when dry, weakly spreading when moist, obovate or short-lingulate, occasionally wider than long, short, ca. 0.4–0.5 µm in length, upper lamina broadly and deeply concave, margins plane, entire or dentate at apex; apex usually broadly and often also sharply apiculate, usually cucullate; base not differentiated in shape; costa percurrent or occasionally ending 1–3 cells below apex, costa with lamina inserted nearly laterally, superficial cells papillose, quadrate and usually bulging ventrally, dorsally elongate, sharply papillose near apex dorsally, ca. 3 rows of cells across costa ventrally at midleaf, costal transverse section semicircular to circular, stereid band weak and rounded in shape, ventral epidermis present, often strongly bulging, dorsal epidermis present or absent, guide cells 2 in one layer or absent, hydroid strand absent, costa often expanded as a large, ventrally bulging, rounded, oil-rich excrescence nearly as wide as the leaf but this affecting only the deciduous, uppermost leaves; upper laminal cells quadrate, ca. 13 µm in width, 1:1, walls thin, superficially weakly convex on both sides of lamina; laminal papillae present only dorsally near costa at leaf apex, 1–3 per lumen, simple, hollow to solid; basal cells only weakly differentiated, quadrate to short-rectangular, ca. 15 µm in width, 1–2:1, walls thin. Apparently dioicous (naked axillary archegonia reported in original description). Sporophytes and androgametophytes unknown. Laminal KOH color reaction red. (Because of paucity of available material, details of the costal section are from the original description and illustrations.)

Found on soil or thin soil over limestone in dry areas of southern Australia.

Stonea oleaginosa has a swollen, oil-rich lenticular knob on the ventral surface of the upper costa of the very uppermost leaves on the stem. Leaves farther down on the stem lack this excrescence, but instead have protruding, bottle-shaped, papillose cells on the ventral costal surface much like those on the costa of Crossidium aberrans. Stonea is entirely red in KOH and has plane margins, features absent in Crossidium. As in the case of Gymnostomiella ((q.v.), the leaves of Stonea may have attained their general lack of distinctive characters through paedomorphosis. This genus is probably closely related to Syntrichia; S. caninervis has a similar spinose-papillose dorsal surface of the costa, a very small immature habit, and similar oil globules in its upper laminal cells, but Stonea differs by its obovate leaves with plane margins and upper laminal cells smooth except for the extreme upper marginal cells and the tip of the costa. There is some similarity with Chenia leptophylla, which also has a strongly papillose and sharply apiculate leaf apex, but which has larger laminal cells and a very narrow costa.

Literature: Stone (1978).

Number of accepted species: 1.

Species examined: Stonea oleaginosa (MELU).