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

380 SALVINIACEAE/SALVINIA
Marsileaceae—Marsilea, Pilularia, and Salviniaceae—Salvinia). These groups are quite distinct
morphologically, and traditionally the marsileaceous (Marsilea and Pilularia) and
salviniaceous (Azolla and Salvinia) lines were considered to have evolved independently from
different homosporous fern ancestors. However, all three living heterosporous water fern families
appear to comprise a monophyletic group as suggested by recent morphological, fossil, and
molecular evidence (Rothwell & Stockey 1994; Hasebe et al. 1995; Pryer 1999).
FAMILY RECOGNITION IN THE FIELD: small free-floating aquatics with leaves in groups of three
(two leaves floating, nearly rounded to elliptic, entire, with conspicuous branched hairs; one
leaf submerged, finely dissected, root-like).
REFERENCES: Schneller 1990b; Nauman 1993d.
SALVINIA Séguier
FLOATING FERN, WATER-SPANGLES, WATER-MOSS
Free-floating aquatics (can be trapped on mud when water levels fall); roots absent; stems
creeping; leaves dimorphic, in groups of three—two floating and one submerged; floating leaves
green, simple, unlobed, nearly round to oblong or elliptic, entire, obtuse or notched apically, the
upper surface with numerous whitish, multicellular, papillate hairs, these having a single base
and four branches, the lower surface with unbranched hairs; submerged leaves finely dissected,
root-like; sporangia (either microsporangia or megasporangia) in sporocarps (formed by membranous
indusia surrounding the sori) on submerged leaves, indehiscent, dispersed when the
sporocarps decay (but plants usually infertile and reproducing vegetatively).
AA genus of ca. 10 species of floating ferns (Nauman 1993d). The hairs on the upper leaf surfaces
trap air, causing the plants to right themselves if turned over in the water (Lellinger 1985).
The leaves are unusual in that the upper sides of the floating leaves (the sides visible to an observer),
which appear to face the stem axis, are actually morphologically the lower (= abaxial)
leaf surfaces (Croxdale 1978, 1979, 1981; Nauman 1993d). Some species have become serious
aquatic weeds, particularly on man-made reservoirs and in irrigation systems (Schneller
1990b). Because of their potential threat to aquatic ecosystems, all species of the genus are prohibited
in Texas (Harvey 1998). While the floating leaves of the two species discussed below are
often different in size, crowding or low-light conditions tend to reduce leaf size, making the
character less useful in determining species (Lellinger 1985). (Named for Professor Antonio
Maria Salvini, 1633–1729, Italian botanist and professor of Greek at Florence)
REFERENCES: Herzog 1935; Weatherby 1937; Morton 1967c; Mitchell & Tur 1975; Croxdale 1978,
1979, 1981; Forno 1983; Jacobsen 1983; Thomas & Room 1986; Moran 1992; Hatch 1995; Jacono
1999a, 1999b, 1999c, 2001a, 2001b; O’Kennon et al. 1999; Garbari et al. 2000; Jacono et al. 2001;
Wood et al. 2001.
1. Hairs of the upper surface of floating leaves 4-branched, the branches free at their tips (use
magnification; sometimes difficult to observe on herbarium specimens); floating leaves usually
6–15 mm long, usually not folded; lower surface of floating leaves 6 covered with hairs __________ S. minima
1. Hairs of the upper surface of floating leaves 4-branched, the branches joined at their tips (resembling
a “cage” or an “egg beater”); floating leaves usually 13–30(–38) mm long, often folded;
lower surface of floating leaves sparsely hairy or � glabrous except for hairs along the midvein
________________________________________________________________________________ S. molesta
Salvinia minima Baker, (least, smallest), COMMON SALVINIA, WATER-SPANGLES, FLOATING FERN.
Stems 1–6 cm long; floating leaves usually 6–15 mm long, rounded to cordate basally, obtuse or
notched apically, usually not folded. Lakes and other aquatic habitats; Jasper (BAYLU), Jefferson
(TAES), Robertson (Turner et al. 2003), Orange, Tyler (R. Helton, pers. comm.), and probably
Newton and Sabine (it is known from the LA side of Toledo Bend—R. Helton, pers. comm.) cos.;
naturalized in scattered localities across se U.S. (AL, AR, GA, FL, LA, OK, and TX), also MA, MD,