Blindiadelphus subimmersus (Lindb.)

Fedosov, Vladimir E., Fedorova, Alina V., Ignatova, Elena A. & Ignatov, Michael S., 2017, A revision of the genus Seligeria (Seligeriaceae, Bryophyta) in Russia inferred from molecular data, Phytotaxa 323 (1), pp. 27-50 : 43

Blindiadelphus subimmersus (Lindb.) Fedosov & Ignatov

The short setae have traditionally been considered as the essential character of Seligeria subimmersa (cf. Vitt 1976), though Nyman (1961) found that this feature is rather variable, as he revealed several specimens of S. subimmersa with setae longer than 2 mm. Thus he concluded that additional comparative study of S. subimmersa and S. diversifolia is needed. Indeed, most specimens studied by us of B. subimmersus have remarkably widened perichaetial leaves thus resembling B. diversifolius , while the more or less differentiated alar cell group is not stable in B. subimmersus and occasionally occurs in B. diversifolius and B. sibiricus . We studied the isotype specimen from H ( FINLAND, Kuusamo, Kitkajoki, in rupe, 19 August 1867, Fr. Silen, # HA.H4221204) for morphology and found that it also represents the morphotype with rather long setae, about 2 mm. An identical specimen (in terms of morphology) from Orulgan Range, Yakutia was also included in the molecular study.

The position of the B. subimmersus clade differs in trees inferred from trn L and ITS sequences. Somewhat similar situations, though with supported conflicts between topologies inferred from nuclear and chloroplastic markers, were recently revealed in other groups of Grimmiales ( Hernández-Maqueda et al. 2008, Ignatova et al. 2016) and considered as reticulation. Having a circumpolar distribution, B. subimmersus cannot be considered as a putative hybrid of recent origin. The ITS tree suggests B. diversifolius as one parent, while the other parent is not apparent.

Unlike other species from clade A, both B. diversifolius and B. subimmersus share the trend to sharply differentiated perichaetial leaves with strongly widened basal portion, abruptly narrowed to rather short upper portion. While the seta length is unreliable for differentiation of B. subimmersus and B. diversifolius , there are other distinctions between them: (1) leaves twisted when dry in B. subimmersus vs. straight to slightly curved in B. diversifolius ; (2) quadrate cells, which descend along the leaf margin, reach the insertion and occupy almost all of the leaf lamina except for a few rows in the basal leaf portion alongside the costa in B. subimmersus vs. elongate throughout the width of the basal leaf portion in B. diversifolius ; (3) costae filling subulate, blunt, strongly canaliculate to cucullate leaf apices in B. subimmersus vs. ending below leaf apices (excepting perichaetial leaves), with laminae reaching leaf apices in B. diversifolius ; (4) lamina partially bistratose along upper leaf margin (cf. Ignatov et al. 2017) in B. subimmersus vs. unistratose throughout in B. diversifolius . Thus, we found B. subimmersus acceptable at the species level.