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

930 POACEAE/ERAGROSTIS
with few-flowered spikelets are extremely similar morphologically and difficult to distinguish
(e.g., E. intermedia, E. lugens). According to Clayton and Renvoize (1986), some species are “very
close” to Sporobolus. Recent studies (Hilu & Alice 2000, 2001; Van den Borre & Watson 2000)
raise questions about the monophyly of Eragrostis as traditionally delimited; a number of small
segregate genera need to be included for Eragrostis to be monophyletic (Ingram & Doyle 2004).
(Derivation of name uncertain; according to Peterson (2003a), “Nathaniel Wolf (1776), the person
who first named Eragrostis, made no statement concerning the origin of its name. Clifford
(1996) provides three possible derivations: from eros, ‘love’, and Agrostis, the Greek name for an
indeterminate herb; from the Greek er, ‘early’ and agrostis, ‘wild,’ referring to the fact that some
species of Eragrostis are early invaders of arable land; or the Greek eri-, a prefix meaning ‘very’
or ‘much,’ suggesting that the name means many-flowered Agrostis. Many authors have stated
that the first portion of the name is derived from eros, but none have explained the connection
between Eragrostis and passionate expressions of love, the kind of love to which eros applies.”)
(subfamily Chloridoideae, tribe Cynodonteae)
REFERENCES: Nicora 1962; Koch 1974, 1978; Witherspoon 1977; Perry & McNeill 1986; Reeder
1986; Van den Borre & Watson 1994; Peterson et al. 1997; Poverene & Voigt 1997; Hilu & Alice
2000; Peterson 2003a; Ingram & Doyle 2004.
1. Culms definitely creeping, rooting at nodes; plants mat-forming annuals; flowering culms to
only 25 cm tall (usually less).
2. Plants dioecious (spikelets either all staminate or all pistillate); anthers 1.2–2.2 mm long; lemmas
(1.8–)2.1–4 mm long, usually with short hairs along the veins; styles long-exserted from
lemma and palea, often persistent and conspicuous (with a hand lens) as thread-like
structures ______________________________________________________________________ E. reptans
2. Plants with perfect florets; anthers 0.5 mm or less long; lemmas 1.5–2(–2.3) mm long, glabrous;
styles not exserted ______________________________________________________ E. hypnoides
1. Culms erect or ascending, sometimes spreading at base, not rooting at the nodes (rarely rooting
at lowest nodes); plants clump-forming annuals or perennials; flowering culms usually much
more than 25 cm tall.
3. Spikelets extremely small, 1–2 mm long, with 1(–3) floret; species introduced in Brazos Co.
and known in East TX only from there _______________________________________________ E. airoides
3. Spikelets (1.5–)2 mm long or longer (often much longer), with 2–many florets; including species
widespread in East TX.
4. Main branches of inflorescence bearing spikelets to very base or nearly so; inflorescences
usually relatively dense and narrow (but open in E. sessilispica).
5. Spikelets sessile, widely spaced on long, widely spreading, unrebranched primary
branches _______________________________________________________________ E. sessilispica
5. Spikelets nearly short-pedicelled or sessile, closely crowded on short or long branches
(if long, then stiffly ascending).
6. Spikelets 3–10 mm wide, usually � 2 times as long as wide, strongly flattened, disarticulating
below the glumes, each spikelet falling as an intact unit; introduced species
rare in East TX _______________________________________________________ E. superba
6. Spikelets 5 mm or less wide (often much narrower), usually � 2 times as long as wide
(often many times), usually slightly to strongly flattened, disarticulating internally, each
spikelet not falling as an intact unit; including widespread and abundant native and
introduced species.
7. Spikelets (1.5–)2–3(–3.8) mm long, often so small and densely arranged that the
individual spikelets are not discernible without close inspection.
8. Inflorescences 15 cm or more long, the main branches usually much longer
than 3 cm, stiffly appressed to ascending, but the inflorescence obviously
branched; palea keels glabrous or minutely scabrous, the scabrosities 0.2 mm
or less long ________________________________________________________ E. japonica