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

ISOETES/ISOETACEAE
323
DIVISION LYCOPODIOPHYTA
CLUB-MOSSES, SPIKE-MOSSES, QUILLWORTS
AA group of 1,200–1,250 species in 12–17 genera arranged in three families (Flora of North
America Editorial Committee 1993). Members of all three families, Isoetaceae, Lycopodiaceae,
and Selaginellaceae, occur in East Texas. Extinct members of this ancient division (e.g.,
Lepidodendrales—scale trees to 55 m tall) were dominants of the Carboniferous forests that
formed present-day coal deposits. It is one of the oldest plant groups, dating to the Lower Devonian
Period (408–360 million years ago) (Benson 1979; Bell & Woodcock 1983; Jones &
Luchsinger 1986; Raven et al. 1986; Moran 2004). The Lycopodiophyta are characterized by microphylls
(= leaves with a single vein), and the group is sometimes referred to as the
Microphyllophyta (Woodland 1997). Chloroplast DNA data (Raubeson & Jansen 1992) show
that the living Lycopodiophyta (Ly copodium sensu lato, Selaginella, and Isoetes) share with the
bryophytes (mosses, liverworts, hornworts) a particular mutation in contrast to all other vascular
plants. These data, other molecular studies, and morphological evidence all indicate that
among living vascular plants the lycopsids are the basal lineage (Raubeson & Stein 1995;
Kenrick & Crane 1997; Doyle 1998; Duff 2000; Pryer et al. 2001). However, the situation is not
completely resolved since gene sequence data are ambiguous, with the Lycopodiophyta sometimes
appearing polyphyletic (e.g., Manhart 1995; Boivin 1996; Wolf 1997).
REFERENCES: Benson 1979; Bell & Woodcock 1983; Jones & Luchsinger 1986; Raven et al. 1986;
Snyder & Bruce 1986; Bold et al. 1987; DiMichele & Skog 1992; Wagner & Smith 1993; Raubeson
& Jansen 1992; Raubeson & Stein 1995; Woodland 1997; Duff 2000.
ISOETACEAE Rchb.
QUILLWORT FAMILY
AA monogeneric, nearly cosmopolitan family of ca. 150 species (Taylor et al. 1993).
QUILLWORTS range from perennial evergreen aquatics to ephemeral terrestrials. They are superficially
unlike other Lycopodiophyta, but as in other members of the division, the leaves have a
single vein; ligules (= minute, tongue-like, basal protuberance on a leaf) are present as in the
Selaginellaceae; spores are differentiated into microspores and megaspores. The long linear
leaves have a resemblance to the quills of feathers formerly used as writing implements. This in
combination with the Old English, wort, (from Anglo-Saxon: wyrt), an herb, root, or plant, gives
rise to the common name.
FAMILY RECOGNITION IN THE FIELD: the two East TX species are tufted, wet area plants with a
corm-like rootstock and hollow quill-like leaves, giving them the appearance of garden chives,
tiny green onions, or small sterile spike-rushes; sporangia are in the leaf bases.
REFERENCES: Pfeiffer 1922; Correll 1949, 1956, 1966a; Jermy 1990a; Taylor et al. 1993.
ISOETES L. QUILLWORT
Plants tufted perennials, terrestrial or becoming so, superficially resembling garden chives (Allium,
Alliaceae) or a sterile spike-rush (Eleocharis, Cyperaceae); rootstock corm-like, globose,
2-lobed, persisting after the leaves die back during hot dry weather; leaves quill-like, linear, hollow,
tightly clustered together; sporangia solitary, embedded in broadened basal cavity of leaf
with ligule inserted above, often partly covered by a velum (= thin flap of tissue); spores of 2
types (plant heterosporous), the megaspores often with faint wrinkles or tubercles, the microspores
much smaller.
ASpecies are often difficult to identify, sometimes requiring microscopic examination of
spores, and interspecific hybrids are known. The spores are reported to be dispersed in the excreta