Two new species of Martensia (Delesseriaceae, Rhodophyta) from Kenting National Park, southern Taiwan

Two new species of Martensia (tribe Martensieae, subfamily Nitophylloideae) are described from Kenting National Park, southern Taiwan. Martensia lewisiae sp. nov. can be separated from all other species of Martensia by the formation of extensive mats from a creeping system of prostrate and overlapping blades attached by basal and marginal haptera, and by the formation of a weakly developed network only in mature reproductive thalli. Martensia formosana sp. nov. is fan-shaped, consisting of one to three ftabellate blades attached by a few small discoid holdfasts, with a network consisting of a single continuous band that extends over 60–80% of the blade. It is distinguished by the presence of tetrasporangial sori on primary longitudinal lamellae and bladelets (secondary lamellae) borne on the cross-connecting strands. As is typical for Martensia, growth in both species is diffuse, initiated by the meristematic activity of multinucleate marginal and intercalary cells. A network is initiated from a row of transformed marginal cells, each of which cuts off an apical initial that divides to form the longitudinal lamellae and reform the margin of the blade. Cross-connecting strands develop unidirectionally (M. lewisiae) or bidirectionally (M. formosana) from the primary lamellae. Spermatangial sori are borne on both sides of the blade (M. lewisiae) or on the longitudinal lamellae (M. formosana). Procarps and cystocarps are formed along the margins of the blade and longitudinal lamellae (M. lewisiae) or in the network at the intersections of longitudinal lamellae and cross-connecting strands (M. formosana). Postfertilization fusion cells are absent, and the primary pit connections broaden between gonimoblast cells, which remain distinct and uninucleate. Tetrasporangial sori are borne on membranous parts of the blade and rarely on the network (M. lewisiae) or on primary lamellae and secondary bladelets within the network (M. formosana). Tetrasporangial initials are multinucleate, transformed from cells in monostromatic portions of blades or lamellae. Two well-supported clades were identified in rbcL analyses, one containing M. formosana and the type species of Martensia, M. elegans. and the other containing M. lewisii and a group of species that cluster with M. fragilis. Species richness in Martensia is much greater in Taiwan than previously thought, and the same may be true for other regions of the world.