RIELLA

Riella heliospora Segarra-Moragues, Puche & Sabovljević (2012: 315-316). Type from U.S.A. California: Santa Clara Co., Lake Lagunita, cultivated from sediments collected from the locality on 30 April 2011 and dried 21 September 2011, J.G. Segarra-Moragues, M. Palop-Esteban, J.J. Palop-Esteban and I. Cobos-Sillero. 

Plants 1.8–3 cm, caespitose, unbranched or bifurcate from the base. Dorsal wing 1–3.4 mm wide, deeply lobed. Scales dimorphic; vegetative scales ligulate, linear or lanceolate; propaguliferous panduriform scales. Sexual condition monoicous. Antheridia in groups of 2–4, often solitary, in sinuses of the dorsal wing. Archegonial involucre ellipsoid, blunt at apex, with (7) 8 (9) wings of 272–482 μm wide. (Figure 1)

Figure 1. Photographs of Riella heliospora: (A) habit, (B) position of antheridia (arrows) in plants with sporophytes and (C) female involucres.

Spores 104–127 × 102–124 μm including spines, light brown, tetrahedral, triangular in outline. Distal face loosely covered with 10–16 irregular rows of spines across diameter, smaller papillae absent, distance between spines 5.5–11.5 μm, and (23) 25 (28) projecting spines at periphery at the equatorial plane. Spines (12) 15.79 (21) μm long (4) 5.17 (6) μm wide, apices truncate, dilated, basal membranes interconnecting spines below high, 1.5–5.2 μm, forming perfect reticulations and defining areolae; basal membranes at the equatorial plane 4.7–12.7 μm high, forming wing-like marginal webbing. 

Habitat and distribution: fresh water seasonal lakes. Known only from two Californian populations, Lake Lagunita at the Stanford University Campus (Thompson, 1940, 1941, 1942) and Cache Creek settling basin Sacramento Valley (Doyle and Stotler 2006).

The gametophytes of Riella heliospora are very similar to those of R. affinis. Spore morphology provides the best differentiation between both species. Because of the spores being triangular rather than round in outline, wing-like marginal webbing and a conspicuous triradiate mark on the proximal face, R. heliospora resembles the South African R. purpureospora Wigglesworth (1937:312). However, this species is dioicous and has smooth involucres and unique purple-red spores (Wigglesworth, 1937; Perold, 2000) therefore, confusion with this species is unlikely.