Beard’s Provinces: Northern Province.
IBRA Regions: Dampierland.
IBRA Subregions: Pindanland.
IMCRA Regions: Canning.
Local Government Areas (LGAs): Broome.
Habit and structure. Thallus prostrate with dense lateral branches, robust, mat-forming, dull purple, violet to brown; main axes indeterminate, 20–50 mm long bearing determinate branches 2–3 mm long, with 1–3(–4) orders of alternate branching (0–20 second order determinate branches); two tiers of pericentral cells per axial cell with 5–7(–8) pericentral cells per tier around the
main axes, 5 pericentral cells per tier in fertile and ultimate branches; indeterminate axes and first order lateral branches corticate; polysiphonous except for wholly or partially monosiphonous ultimate and penultimate branches; peripherohaptera associated with bifurcations of indeterminate axes. Indeterminate axes 80–500 µm in diameter, axial cells 60–300 µm long; cortex with
(1–)2–3 orders of cells; superficial cortical cells rectangular to ovoid, 8–30 µm long, 5–15 µm wide; branches arising subdichotomously or laterally at intervals of 1(–4) axial cells. Determinate
branches of 1–3(–4) orders arising at intervals of 1(–2) axial cells; branches other than the first order predominantly ecorticate; ultimate branches of variable diameter, tapering to a monosiphonous filament (2–)6–60 cells long. Peripherohaptera formed on indeterminate axes, adjacent to bifurcations, or (rarely) at random, usually 6–10 cells long prior to contact with the substratum.
Reproduction. Carpogonial branches borne within the polysiphonous intercalary axial cells of ultimate lateral branches; fertile region 2–8(–25) consecutive axial cells long with 1–3(–4) procarps per axial cell; axial cells below the fertile region have (4–)5 pericentral cells per tier and procarpial axial cells 5 per axial cell; the supporting cell produces a sterile group of 2–3 cells prior to fertilisation and the adjacent sterile pericentral cell produces a group of 2–3 cells; the carpogonial branch is (2–)3 cells long. Cystocarps intercalary or subapical, ovoid to globular, 500–800 µm long, 400–700 µm in diameter with a 30–80 µm diameter ostiole; cystocarp walls have 8 longitudinal pericarp filaments with 2–3 two-tiered pericarp pericentral cells per filament cell and 1–2 orders of cortical cells; carposporangia (85–)90–110(–115) µm long, 15–40 µm in diameter, 70–100 per cystocarp. Spermatangial branches 200–400 µm long, 25–150 µm in diameter formed from 8–40 subapical axial cells of ultimate lateral branches; axes below the fertile region are monosiphonous or polysiphonous with 5 pericentral cells per tier; spermatangial branches have 5 pericentral cells around the axial cell, giving rise to two tiers of pericentral cells; each pericentral cell produces (0–)1–2 orders of cortical cells, and all superficial cells are potentially spermatogenous. Tetrasporangia borne in subapical or intercalary stichidia on polysiphonous axial cells of ultimate lateral branches; stichidia 200–1500 µm and 2–20(–25) axial cells long, 120–250 µm in diameter; branches bearing stichidia have 5 pericentral cells per tier; stichidia have 4(–5) pericentral cells per axial cell, each of which gives rise to a tetrasporangium and (2–)3 cover cells; each cover cell divides and subsequently forms several cortical layers; tetrasporangia 30–70 µm in diameter.
Distribution. Widely distributed in tropical and warm temperate seas. Found on tropical coasts of Australia (W. Aust., N. Territory, Qld., and Lord Howe I., N.S.W.) south to latitude 26"s.
Habitat. B. tenella occurs on intertidal rock and mangrove prop roots and pneumatophores. Grows on coral rubble of inshore reefs but mainly on mangrove prop roots and pneumatophores.
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/