Riella choconensis

Segarra-Moragues, José Gabriel, Puche, Felisa & Gleiser, Gabriela, 2019, Study of a new population of the Argentinian endemic species Riella choconensis Hässel (Riellaceae, Marchantiophyta) reveals a novel anatomical structure of the female involucre in Riella, Cryptogamie, Bryologie 20 (12), pp. 131-140 : 138

OF RIELLA CHOCONENSIS

Our detailed study of the morphological traits of this species supplements the original description of the species by Hassel de Menéndez (1987a). The fact that gametophytes are unisexual (i.e. a dioicous species) and that the female gametophytes carry sporophytes contained into smooth involucres distinguishes this species from the Californian R. heliospora Segarra, Puche & Sabovlj. , and the Argentinian R. gamundiae , the only American species of subgenus Trabutiella ( Hässel de Menéndez 1972; Segarra-Moragues et al. 2014). The four American species of subgenus Riella are gametophytically very similar, requiring spore characters for reliable identification. Notwithstanding, here we have revealed for the first time the occurrence of bistratose female involucre walls in Riella . This trait has been rarely observed in the Sphaerocarpales , with a single exception in the mostly southern hemisphere Sphaerocarpos stipitatus Bertero ( Perold 2000a) . Moreover, the female involucres of R. choconensis showed occluded involucre apex, covered by inflated, bulging cells. While this occurs in all six species of subgenus Trabutiella (Segarra-Moragues et al. 2014) , it has not been observed previously in species of subgenus Riella ( Puche & Segarra-Moragues 2013; Segarra-Moragues & Puche 2014). Thus, despite the simplicity of gametophytes, the morphology of female involucres provides a set of highly informative gametophytic traits, which aid to establish taxonomic boundaries between species of Riella .

The spores of the cultured specimens, densely covered in their distal face with long (9.5-15.2 µm) spines, with low or absent basal membranes, undefined areolae and with acute or blunt apices, unambiguously allowed us to identify the specimens as R. choconensis . Other Argentinian species have spores with shorter (4.7-9.4 µm) distal spines ( R. undulata, Hässel de Menéndez 1987b ), have distal spore faces covered with fewer (8-10) rows of longer spines with granulose surfaces ( R. pampae, Hässel de Menéndez 1979 ) or have spores with distal spines with flaring, truncate apices and basal membranes defining areolae ( R. americana, Hässel de Menéndez 1959 ). Based on new morphological data an updated identification key including all species known to date in the American continent is presented.