22. Panicum portoricense Desv. ex Ham.
Pl. 164 g,
h; Map 683
P. columbianum Scribn.
P. acuminatum Sw. var. columbianum
(Scribn.) Lelong
Dichanthelium columbianum (Scribn.) Freckmann
D. portoricense (Desv. ex Ham.) B.F. Hansen & Wunderlin
D. sabulorum (Lam.) Gould & C.A. Clark var. thinium (Hitchc.
& Chase) Gould & C.A. Clark
Plants perennial, without rhizomes,
forming tufts.
Flowering stems 10–60 cm long, erect or spreading, initially unbranched,
becoming much‑branched during the summer and autumn, the nodes and
internodes short‑hairy, the internodes sometimes also with a few
scattered, longer hairs. Foliage in a dense rosette of shorter, somewhat
broader leaves at the base and longer, narrower leaves well distributed along
the main stems, those of the later branches often appearing as axillary
fascicles of even shorter, narrower leaves. Leaf sheaths hairy, at least the
lowermost sheaths usually with numerous, shorter, stiff, appressed hairs mixed
with sparse, longer, softer, spreading hairs, at least some of the hairs with
pustular bases, the ligule 0.5–1.5 mm long, an inconspicuous line or band of
hairs. Leaf blades of the main stems 1–7 cm long, 3–7 mm wide, abruptly rounded
or truncate at the base, relatively thick and stiff, glabrous or sparsely short‑hairy
on the upper surface, usually short‑hairy on the undersurface, some of
the hairs sometimes with pustular bases, the margins somewhat thickened and
with sparse, stiff hairs at the base. Inflorescences 2.5–4.5 cm long, the
earlier ones larger and more open with mostly spreading to loosely ascending
branches (later ones sometimes reduced to small clusters of long‑stalked
spikelets), the branches mostly rebranched 1 or more times, not spikelike or 1‑sided,
the spikelets appearing short‑ to long‑stalked at the tips of the
branches. Spikelets 1.2–2.0 mm long, broadly elliptic to
slightly obovate in outline. Lower glume 0.3–0.6 mm long, 1/4–1/3 as
long as the spikelet, broadly ovate, bluntly to sharply pointed at the tip,
glabrous or sparsely hairy, nerveless or faintly 1–5‑nerved. Upper glume
1.0–1.8 mm long, broadly elliptic‑obovate, rounded at the tip, 5–9‑nerved,
hairy. Lowermost floret sterile and with a reduced, inconspicuous palea, the
lemma 1.0–1.8 mm long, broadly elliptic‑obovate, rounded at the tip, 5–9‑nerved,
hairy. Fertile floret 1.0–1.6 mm long, elliptic, rounded or
bluntly pointed at the tip. Anthers 0.2–0.8 mm long.
2n=18. May–September (vernal), June–November
(autumnal).
Uncommon, known presently only from
a single collection from Taney County (northeastern U.S.
west to Minnesota and Missouri, uncommonly farther south). Savannas, to be
expected in mesic to dry upland forests and glades.
This species has a confusing history of treatment, both
taxonomically and as part of the Missouri
flora. Gould and Clark (1978) treated it as a variety of the South American D.
sabulorum, but subsequent authors have argued that the North and South
American plants are different species (Lelong, 1984, 1986; Hansen and
Wunderlin, 1988). Opinions have varied on the correct name to apply to
materials from the United
States, but P. portoricense appears
to be the oldest epithet that applies to the taxon. In Missouri, Steyermark (1963) excluded the
species, based upon uncertain data on the label of the single collection that
he thought might represent the taxon. Examination of this specimen during the
present study resulted in its redetermination as P. acuminatum var. acuminatum.
Nelson (1982) reported P. columbianum for Missouri
based on a collection of his from Reynolds
County, but that specimen
is also P. acuminatum var. acuminatum. Most recently, Doug Ladd
collected another specimen of this taxon from Taney County that has been
verified as true P. portoricense, and the species is thus reinstated as
a part of the Missouri flora.