Avrainvillea obscura (C.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus with a flabellate or irregularly shaped blade borne on a mostly buried holdfast (when growing in sand or mud), rarely with an emergent holdfast on rock. Emergent part of thallus to 6 cm tall, grey-green to olive-brown (often drying almost black). Holdfast filamentous, extensive, forming a bulbous conglomerate with substratum particles. Blade spongy, subcuneate or irregular, generally entire but occasionally lacerate, sessile or with a short stipe. Structure of blade multistratose, with interwoven cylindrical siphons 25–50 µm diam., these irregularly dichotomously branched, with deep constrictions at dichotomies. Terminal siphons slightly broader, with rounded to clavate apices. Plastids subspherical, ellipsoidal or reniform, 5–7 µm long, each with a pyrenoid.

Distribution. Warmer waters of the Indo-Pacific.

Habitat. Grows in sandy and silty substrata, generally in the intertidal or the shallow subtidal, rarely to a depth of 10–11 m.

[After Huisman, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 121-122 (2015)]