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

322 PSILOTACEAE/PSILOTUM
data from four different genes and morphology, strongly supports the link of Psilophyta with
the Ophioglossaceae and suggests its inclusion within the Polypodiophyta (ferns). As a result,
many pteridologists (e.g., Moran 2004) now consider the Psilotaceae to be a family of ferns.
Nonetheless, because the group differs from all ferns and similar plants in many characters
(Kaplan 1977; Wagner 1977), and until there is a clearer understanding of the evolutionary relationships
of Psilophyta, we are tentatively following a number of authors who continue to recognize
the group as a separate division (e.g., Wagner & Smith 1993; Woodland 1997). Psilotum
nudum is the only species in the division known to occur in North America.
PSILOTACEAE Eichler
WHISK-FERN FAMILY
AA very small family (2 genera, 4–8 species) found worldwide in tropical regions (Thieret
1993) and extending to warm areas. The genus Tmesipteris occurs from se Asia to Australia,
New Zealand, and some Polynesian islands.
Family recognition in the field: the only species in the flora is a dichotomously branched, leafless,
spore-bearing perennial with green photosynthetic stems 0.5 m or less tall.
REFERENCES: Bierhorst 1977; Cooper-Driver 1977; Gensel 1977; Kaplan 1977; Wagner 1977; White
1977; Kramer 1990a; Thieret 1993; Manhart 1995; Pryer et al. 1995; Wolf 1997; Vangerow et al.
1999; Rothwell 1999; Schneider & Carlquist 2000a; Pryer et al. 2001.
PSILOTUM Sw. WHISK-FERN, FORK-FERN
AA genus of 2 or 3 species (Thieret 1993) with leafless, green, photosynthetic stems. The common
name, whisk-fern, comes from the much-branched leafless stems which give the plant the
appearance of a whisk broom. (Greek: psilos, naked, smooth, or bare, either in reference to the
leafless stems or to the “naked” sporangia which are not covered by indusia)
REFERENCES: Correll 1960; Lodwick 1975.
Psilotum nudum (L.) P. Beauv., (bare, naked), whisk-fern. Terrestrial, sometimes epiphytic perennial
with coral-like, short-creeping, rhizoid-bearing, branched rhizomes; roots absent (but rhizoids
absorptive); aerial shoots erect to ascending, to 25(–50) cm tall (greenhouse material often
more robust), photosynthetic, dichotomously branched 3–5 times, 3(–several)-ridged; stem appendages
(= enations) veinless, scale-like, minute, 0.7–3 mm long; leaves absent; spores all of 1
kind (plants thus homosporous), produced in sporangia, these fused in groups of (2–)3 to form
� globose, (2–)3-lobed synangia; synangia 2–3 mm wide, solitary in axils of minute shoot appendages;
gametophytes subterranean, with mycorrhizal fungi; chromosome number variable,
n = 46–56, 104, 210 (Thieret 1993). Low woods, swamps, wet areas, wet peaty humus, and around
bases of trees and stumps; Hardin Co. in s part of Pineywoods (TEX, Correll 1960—this collection
from the Big Thicket was the first in the state; Lance Rosier led Correll to the location) and
Freestone Co. in the Post Oak Savannah (TEX; Lodwick 1975); se U.S. from NC s to FL w to AR
and TX, also AZ. Sporulating summer. [Lycopodium nudum L.] Grown as an ornamental in some
areas, particularly Japan (Hyam & Pankhurst 1995); it can be a minor weed in greenhouses
(Thieret 1993). Although extremely rare in TX, in some areas of the U.S. (e.g., FL) it can appear as
a weed. The species can be epiphytic in situations such as on tree bases, stumps, old logs, or tree
forks with accumulated debris (Nauman et al. 2000; Nelson 2000). The whisk broom or “leafless
twig” appearance of the whisk-fern is nearly unique among pteridophytes (Nelson 2000).
While not officially designated as such (e.g., TOES 1993; Carr 2002d; Poole et al. 2002), because
of its limited distribution in the state, we consider this species to be of conservation concern in
TX. The rare (and often transitory) occurrence of certain pteridophytes beyond the margins of
their main range (e.g., Psilotum in TX) has sometimes been attributed to transport of spores by
major storms or hurricanes (J. Peck, pers. comm.). �