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

MARSILEA/MARSILEACEAE 353
etation (Nauman 1993a). It is ranked as a category I species on the Florida Exotic Pest Plant
Council’s (EPPC) 1999 List of Florida’s Most Invasive Species (Nauman et al. 2000). � I m/291
MARSILEACEAE Mirb.
WATER-CLOVER OR PEPPERWORT FAMILY
Plants aquatic or of very wet habitats; stems (rhizomes) long-creeping; leaves scattered along
the stems, long-petioled and palmately divided into 4 pinnae or else filiform and lacking expanded
blades; sori contained in sporocarps (= hard bean- or pea-like structures which are apparently
highly modified pinnae) on stalks from near base of petiole; sporangia of 2 kinds
within the same sorus, the megasporangia with 1 megaspore, the microsporangia with numerous
microspores.
AA nearly cosmopolitan family of 3 genera and ca. 50 species (Johnson 1993a). Three families
of heterosporous water ferns occur in East TX (Azollaceae—Azolla, 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, based on recent morphological, fossil, and molecular evidence, all three
living heterosporous water fern families are considered to comprise a monophyletic group
(Rothwell & Stockey 1994; Hasebe et al. 1995; Pryer 1999).
FAMILY RECOGNITION IN THE FIELD: plants of wet areas with leaves resembling a 4-leaf clover (in 1
species apparently rare in East TX the leaves thread-like and � resembling those of a grass);
sori in hard, bean- or pea-like structures near the base of the petioles.
REFERENCES: Correll 1956, 1966a; Kramer 1990c; Johnson 1993a; Lesho 1994; Pryer 1999;
Schneider & Carlquist 2000b.
1. Leaf blades resembling a 4-leaf clover, palmately divided into 4 narrowly to broadly cuneate (=
wedge-shaped) pinnae ______________________________________________________________ Marsilea
1. Leaves filiform, very narrow, somewhat grass-like in appearance, without expanded blades ________ Pilularia
MARSILEA L. WATER-CLOVER, PEPPERWORT
Small plants, aquatic or of wet habitats, often forming dense colonies; leaves long petiolate with
blades palmately divided into 4 pinnae; sporocarps on stalks, the tip of stalk often protruding
as a bump or tooth (proximal tooth), a second distal tooth sometimes present on sporocarps
beyond the attachment point of the stalk.
AA nearly cosmopolitan genus of 45 species (Johnson 1993a). The leaves, with 4 pinnae (=
leaflets), have a superficial resemblance to those of CLOVER; young plants can have unlobed
leaves like Pilularia. � An Australian member of the genus, the NARDOO FERN, (M. drummondii
A. Braun), is particularly rich in the enzyme thiaminase (which breaks down vitamin B1—thiamine)
and is reported to have caused the suffering and death of members of the first scientific
expedition to cross Australia from south to north (1860–61). Upon running out of food, the explorers
ate the fern, which was known to be consumed by aborigines (but specially prepared by
them). The consumption of the inadequately prepared fern resulted in beriberi (vitamin B1 deficiency)
affecting almost all members of the expedition. They experienced weakness, emaciation,
partial paralysis of the legs, nerve damage, and in some cases death. The fatal poisoning of
large numbers of Australian sheep by NARDOO FERN has also been reported (Earl & McCleary
1994; Moran 1995, 2004; Bruneton 1999). The sporocarps of Marselia are extremely durable and
resistant to water loss, and spores may remain viable for up to 130 years (Johnson 1985; Moran
1995). When the sporocarp is moistened, the gelatinous interior takes up water and a worm-