Bonnemaisonia geniculata N.L.Gardner (BC)

This species forms a distinctive but rare element of the (semi)exposed west coast flora. Gametophytic individuals are ghostly pink in colour when observed in situ (Featured image above), 10-20 cm tall and flattened with a percurrent central axis lending the fronds a feathery appearance (Image A). A closer view reveals the regularly-alternating, opposite determinate (spine-like) and indeterminate branches (Image B). Whole mount reveals the dome-shaped apical cells from which the uniaxial development takes place (Image C). The cystocarps (postfertilization development) terminate modified indeterminate branches and are consequently positioned alternately on the axes (Image D) being broadly ovate with an obvious ostiole (Image E). Spermatangia are on separate individuals (dioecious) and similarly form on modified indeterminate branches (Image F) forming a near continuous surface covering of these axes (Image G). The presumably filamentous tetrasporophyte has not been collected in our waters to date, but we have documented them for the congener Bonnemaisonia hamifera Hariot.

We have only nine records of this beautiful species for Canada, these confined to northern Vancouver Island (n = 1) and Haida Gwaii. Individuals were collected from low intertidal pools to the subtidal (10 m) most commonly epiphytic on other species of red algae. This is a fairly unique species in the flora and can easily be identified. To the untrained eye confusion with Cumathamnion decipiens (J.Agardh) M.J.Wynne & G.W.Saunders is possible, but that species lacks the distinctive branching pattern of B. geniculataBonnemaisonia californica Buffham overlaps in range with B. geniculata, but that species is more delicate, has narrower axes (typically <2 mm), and produces hook-like structures as is typical of many species in this genus. 

Image A. Subtidal (3 m on Odonthalia floccosa (Esper) Falkenberg) collection from Bowles Pt., Gwaii Haanas (GWS030652).

Image B. Close up of the regular opposite branching with alternation of the determinate spine-like (arrows) and indeterminate branches (GWS030652).

Image C. View of a dome-shaped apical cell at the tip of a vegetative axis (subtidal (10 m) on Odonthalia floccosa (Esper) Falkenberg from Cape Knox, Haidi Gwaii; GWS036874).

Image D. Cystocarps (arrows) formed alternately along the axes terminating modified indeterminate branches of a female gametophyte (subtidal (7 m) on Hymenena sp., Cape Know, Haida Gwaii; GWS038981).

Image E. Cystocarps are broadly ovate with an obvious ostiole (GWS036874).

Image F. Modified indeterminate branches coated in spermatangia on a male gametophyte (GWS030652).

Image G. Close up view of the spermatangia coating their bearing axis (GWS030652).