Lagarosiphon

Submerged (except for flowers during anthesis), dioecious, rooted herbs from a perennial rhizome; stems long, terete, leafy; branches arising from inside a spathe next to a flower; leafy apices compact; internodes elongating later. Leaves alternate, subopposite or whorled, widely spaced below, dense above, linear to linear-lanceolate; margin dentate with unicellular teeth; tissues of lamina differing in each species, with 2 minute axillary scales (intra-vaginal squamulae). Male inflorescence axillary; spathe valves fused, obovate, ovate or lanceolate, compressed or cup-shaped, dentate; axis (rudimentary scape) producing many pedicellate flowers (up to 50 or more) consecutively; buds become detached and rise to surface (because of an enclosed air bubble) where they expand and recurve suddenly to form a bell-shaped, floating flower; perianth 3 + 3, outer segments slightly narrower; stamens 3; filaments ultimately parallel to water surface with anthers at right angles to them; each anther gives rise to 16 pollen grains (4 per pollen sac); pollen grains large; staminodes 3, longer than stamens, papillate, usually coloured above, joined at top (acting as a sail). Female inflorescence axillary; spathe valves fused, narrowly oblong, ovoid or cylindrical, entire or toothed, containing 1-3 flowers; perianth tube exserted laterally near apex of spathe, lengthening (giving off gas bubbles buoying it up) until flower reaches surface of water (ultimate length of flower varies with species); limb 6-lobed; staminodes 3, minute, filiform; ovary with 3 parietal placentas; styles 3, adnate to perianth tube, each divided into 2 long, papillate, often brightly coloured, stigmatic arms; ovules 6-30, orthotropous, funicle short or long, straight or bent. Fruit a capsule protruding from torn spathe (the larger inner spathe valve bursting along midrib), rostrate (persistent perianth base forming a beak) ultimately becoming mucilaginous and disintegrating. Seeds few to many, cylindrical, shortly stipitate, apex acute, closely ribbed or honeycombed, buoyant at first, sinking later. x = 11 (7, 10-1 report each) (polyploidy).