keys to the vascular plants of east texas - Botanical Research ...

WOODWARDIA/BLECHNACEAE 339
1. Plants usually 1–1.5 cm long, pinnately branched from a central axis, dichotomously branched
only at periphery; megaspores pitted, sparsely covered with a few long filaments; leaves slightly
to greatly imbricate, the upper lobes usually at least 0.7 mm long _________________________ A. mexicana
Azolla caroliniana Willd., (of Carolina), MOSQUITO FERN, WATER FERN, CAROLINA MOSQUITO FERN,
EASTERN MOSQUITO FERN. Plant fertile only infrequently. Still water of ponds, lakes, or slowmoving
streams or stranded on mud; sporadically but widely scattered in e 1/2 of TX (since
this species has long been considered to be the only one in East TX, some records may be the
result of confusion with A. mexicana—see discussion below); B.C., Ont., and e U.S. from NH s to
FL w to SD and TX. Sporulating summer–fall. Scanning electron micrographs of the megaspore
apparatus of this and the following species can be seen in Perkins et al. (1985) and Lumpkin
(1993). Where found, this species is often abundant, and huge numbers of individuals can at
certain times of the summer turn the surface of ponds a striking red color. Fertile specimens are
rarely collected (Nauman et al. 2000). According to Correll (1956), “Its occurrence in remote locations
is doubtless due to its dissemination, in part, by water-fowl.” The species is commonly
cultivated as an aquatic ornamental in aquaria and decorative pools (Lellinger 1985). m/277
Azolla mexicana Schlect. & Cham. ex C. Presl, (of Mexico), MEXICAN MOSQUITO FERN. Similar to
A. caroliniana and distinguished as in the key above; frequently fertile. Still waters; TX distribution
unclear and no county distribution map is provided; included based on range map in
Peck and Taylor (1995) showing this species nearly throughout AR, including immediately adjacent
to the ne border of East TX, and on the range map in Lumpkin (1993) showing it in OK
immediately adjacent to the n border of East TX; B.C. and widespread in c and w U.S. Sporulating
summer–fall. While this species has not previously been considered to be in East TX, there
has long been confusion between this and A. caroliniana (J. Peck, pers. comm.). Lumpkin (1993)
also stressed that because of inconsistent characters used in the past to identify Azolla species,
“Literature that attributes a particular species of Azolla to a particular state or province must
be questioned. …” Further work needs to be done to clarify the distribution of these two similar
species in East TX. Azolla mexicana was erroneously reported to be “generally less cold tolerant”
and to have “a narrower environmental range than A. caroliniana” (Lumpkin 1993), but it
occurs in the upper Mississippi River northward to Minneapolis-St. Paul, MN. The species is occasionally
cultivated (Lellinger 1985).
BLECHNACEAE (C. Presl) Copel.
CHAIN FERN, DEER FERN, OR MIDSORUS FERN FAMILY
AA family of ca. 10 genera and ca. 250 species (Cranfill 1993b); it is mostly tropical and s temperate
except for the n temperate Woodwardia. Family name from Blechnum, DEER FERN, a
mostly tropical, especially s hemisphere genus of ca. 220 species. (Greek: blechnon, classical
name for ferns in general)
FAMILY RECOGNITION IN THE FIELD: sori discrete, linear-oblong, in a chain-like row along each
side of the midvein of a pinna or pinnule; indusia attached by their outer margin, opening toward
midvein.
REFERENCES: Kramer et al. 1990a; Cranfill 1993b.
WOODWARDIA Sm. CHAIN FERN
Terrestrial; stems (rhizomes) in East TX species long-creeping, with leaves scattered along the
stems; leaves monomorphic or dimorphic, deciduous, the blades 1-pinnatifid or 1-pinnate; sori
discrete, linear-oblong, in a single chain-like row along each side of the midvein; indusia attached
by their outer margin, opening on side next to midvein, often obscured by dehisced (=
opened) sporangia.