Azolla filiculoides

Azolla filiculoides Lam.
(Latin: filicula, diminutive of filix, fern, and Greek: -eides, -oides, like or having the form of, the type description saying it has the aspect of a very small fern)

Local names: western mosquito fern

Plant ranging from green or yellowish green to with red margins or dark red; stems } pinnately branched from a central axis, pseudodichotomously branched only at periphery, prostrate and 1–3 cm long when immature, becoming nearly erect when mature and crowded and sometimes to 5 cm or more long; largest hairs on upper leaf lobe with only 1 cell; megaspores with raised hexagonal markings/angular bumps (papillae), with sparse to moderate tangled filaments; 2n = usually 44, rarely 66 (Stergianou & Fowler 1990). Quiet water; Jeff Davis Co. (Correll 15559, TEX-LL, annotated by V.M. Bates and T. Reeves); Johnston (1990) included A. filiculoides for TX pointing out that “Jeff Davis Co. material was referred to this species by Reeves and by Vernon M. Bates Jr. in 1980.” It should be noted that Bates studied Azolla and also published a report of A. filiculoides from Georgia based on SEM examination of megaspores (e.g., Bates & Browne 1981). B.C. in Canada s through w U.S. from WA to OR, CA, and AZ to extreme w TX; also reported for GA and NY (Bates & Browne 1981), the last two locations possibly the result of artificial introductions; native from w North America (including Mexico) to South America, but widely naturalized in the Old World. Sporulating usually in late spring. Yatskievych and Windham (2008a) noted that “Populations of A. filiculoides in Arizona are uncommon and sporadic. Waterfowl move the plants around and eventually it may be discovered at other sites in the state.” Given the relative proximity of Jeff Davis Co. to AZ and the fact that Azolla filiculoides is transported by waterfowl, it is not surprising that a collection of the predominantly western A. filiculoides was made in one of the westernmost counties of TX; collectors should be on the lookout for this species. Velaspino (1993) noted that this species “is cold tolerant, surviving even in fragmented parts under thin ice. It usually reaches a climax population in late spring, becomes fertile, collapses, and is replaced by other more heat-tolerant aquatics such as Lemna spp.” Western mosquito fern was introduced into the United Kingdom by at least the late 1800s and became a problematic invasive; the frond-eating weevil, Stenopelmus rufinasus, was imported from FL in 1995 and has had “remarkable success” in reducing populations in the British Isles ( 2010). Since this species is known from only one collection in TX, we consider it to be of conservation concern in the state.

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