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

CYPERACEAE
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become split by growth of culm), with or without a scaly ring or fringe of hair (ligule) at junction
of sheath and blade on upper (inner) side, and a usually elongate blade (leaves all reduced
to inconspicuous sheaths in Eleocharis and some Cyperus and Scirpus); inflorescences various
(umbellate in Cyperus and Fimbristylis and less distinctly so in some other genera); flowers
(often referred to as florets) perfect or unisexual (in Carex and Scleria), each subtended by a
single (rarely 2) scale-like bract (these bracts often referred to as floral scales or in this treatment
as scales of spikelets or simply scales), without perianth or perianth reduced to bristles or
small perianth scales, solitary or in spikelets (= basic unit of inflorescence, consisting of a shortened
axis and 1–numerous scale-like bracts, the lowermost of which are often empty); stamens
1–3, with anther attached by one end; pistil 1; fruit an achene, usually trigonous or biconvex.
AA large, cosmopolitan (greatest diversity in the tropics but often dominant in cold regions),
taxonomically difficult family of herbs, with over 5,000 species in 104 genera (Goetghebeur
1998); ca. 2,000 of the species are in the huge genus Carex. As such, it is the third largest monocot
family, following the Orchidaceae and Poaceae. The Cyperaceae, with 248 species (7.3% of
the total number of species), is the third largest family in the East TX flora (after Poaceae and
Asteraceae). Floral structures are quite reduced in association with wind pollination, resulting
in a lack of useful taxonomic characters (Yen & Olmstead 2000). Because of the often similar
vegetative parts and reduced reproductive structures, technical characters requiring at least a
hand lens frequently have to be used to distinguish species. Cyperaceae species superficially
resemble both grasses and rushes, and recent evidence suggests a close relationship between
Cyperaceae and Juncaceae (e.g., Simpson 1995; Goetghebeur 1998; Chase et al. 2000; Muasya
2000a; Ball et al. 2002). Phylogenetic analysis indicates that the family is monophyletic
(Muasya et al. 2000a). Some molecular data suggest that Juncaceae and Cyperaceae are sister
taxa (Chase et al. 1995b; Linder & Kellogg 1995) or even that Cyperaceae may be derived from
within Juncaceae, possibly making Juncaceae paraphyletic (Plunkett et al. 1995; Munro &
Linder 1998). According to Plunkett et al. (1995), the “progenitor-derivative relationship of
Juncaceae and Cyperaceae … reveals an additional example of paraphyletic families which presents
a series of taxonomic dilemmas.” A number of similar situations exist (e.g., Brassicaceae
and Capparaceae), and if paraphyletic families are disallowed (as favored by many cladists),
taxonomists are thus faced with wholesale rearrangement of many long established and easily
recognized families—see Appendix 6 for further discussion of these issues. The family is of economic
importance as wildlife food, for woodland grazing, or for erosion control; in n temperate
parts of the world the plants sometimes replace grasses as forage; in TX in the Hill Country and
w part of the state, Carex emoryi L. becomes important for livestock during summer months
(S.D. Jones, pers. comm.); also some are problematic weeds. The sedge family (with ca. 32% of its
species having C4 photosynthesis) is one of only two monocot families (the other is the
Poaceae) with the typical C4 photosynthetic pathway (Soros & Bruhl 2000); this pathway is an
adaptation to prevent water loss and is an advantage in arid environments. Phylogenetic analysis
indicates that the C4 pathway has arisen independently four times in the Cyperaceae (Soros
& Bruhl 2000). (subclass Commelinidae—Cronquist; order Poales—APG II)
FAMILY RECOGNITION IN THE FIELD: grass-like or rush-like herbs with solid internodes, round or
often 3-angled culms (“sedges have edges”), and often 3-ranked leaves; many (but not all) species
grow in wet habitats; flowers small, inconspicuous, without perianth or perianth reduced
to bristles or small scales, subtended by 1 scale-like bract each (or in Carex the female flower
enclosed in a sac-like perigynium), and arranged in very reduced spikes/spikelets. The ± similar
Poaceae (GRASSES) have hollow or solid internodes, round culms, 2-ranked leaves usually
with a ligule, and flowers subtended by 2 scale-like bracts each (lemma and palea); the ± similar
Juncaceae (RUSHES) have flowers with a small 6-parted perianth.
REFERENCES: Svenson 1957; Dahlgren et al. 1985; Goetghebeur 1987, 1998; Tucker 1987; Bruhl et al.
1992; Bruhl 1995; Rolfsmeier 1995; Muasya et al. 2000a, 2000b; Simpson & Inglis 2001; Ball et al. 2002.