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tall beardgrass, tall bluestem

Habit Plants annual or perennial; synoecious, monoecious, or dioecious; primarily herbaceous, habit varied.
Culms

1.3-2.5 m tall, 2-4 mm wide, stiffly erect, not or only sparingly branched;

nodes hirsute, hairs 2-6 mm, stiff, spreading, tan;

internodes glaucous below the nodes.

annual, usually solid, sometimes somewhat woody, sometimes decumbent, often branched above the base.

Leaves

cauline;

ligules 1-3 mm;

blades 20-30 cm long, 4-10 mm wide, glabrous or sparsely pilose near the base.

distichous;

sheaths usually open;

auricles usually absent;

abaxial ligules usually absent, occasionally present as a line of hairs;

adaxial ligules membranous, sometimes also ciliate, or of hairs, sometimes absent;

blades sometimes pseudopetiolate;

mesophyll radiate or non-radiate;

adaxial palisade layer absent;

fusoid cells usually absent;

arm cells usually absent;

kranz anatomy absent or present;

midribs usually simple, rarely complex;

adaxial bulliform cells present;

stomata with triangular or dome-shaped subsidiary cells;

bicellular microhairs usually present, with a long, narrow distal cell;

papillae absent or present.

Panicles

14-25 cm long on the larger shoots, 3-6 cm wide when pressed, oblong, dense;

rachises 10-20 cm, with numerous branches, rachises and branches kinked and wavy at the base from being compressed in the sheath;

branches 2-8 cm, much shorter than the rachises, erect to appressed, with multiple rames;

rame internodes villous on the margins, with 5-8 mm distal hairs.

Inflorescences

ebracteate (Paniceae) or bracteate (most Andropogoneae) panicles, racemes, spikes, or complex arrangements of rames (in the Andropogoneae), usually bisexual, sometimes unisexual;

disarticulation usually below the glumes, frequently in the secondary and higher order axes of the inflorescences.

Spikelets

bisexual or unisexual, frequently paired or in triplets, the members of each unit usually with pedicels of different lengths or 1 spikelet sessile.

Glumes

usually 2, equal or unequal, shorter or longer than the adjacent florets, sometimes exceeding the distal florets;

florets 2(-4), usually dorsally compressed, sometimes terete or laterally compressed;

lower florets sterile or staminate, frequently reduced to a lemma;

upper florets usually bisexual;

lemmas hyaline to coriaceous, lacking uncinate hairs, often terminally awned;

awns single;

paleas of bisexual florets well-developed, reduced, or absent;

lodicules usually 2, sometimes absent, cuneate, free, fleshy, usually glabrous;

anthers 1-3;

ovaries usually glabrous;

haustorial synergids absent;

style branches 2, free and close or fused at the base.

Caryopses

hila usually punctate;

endosperm hard, without lipid;

starch grains simple;

embryos large in relation to the caryopses, usually waisted;

epiblasts usually absent;

scutellar cleft present;

mesocotyl internode elongated;

embryonic leaf margins usually overlapping, rarely just meeting, x = 5, (7), 9, 10, (12), (14).

Sessile

spikelets 4.5-6 mm, ovate;

lower glumes shortly pilose, with or without a dorsal pit;

awns 18-22 mm;

anthers about 1 mm, often remaining in the floret, light brown.

Pedicellate

spikelets 3.8-4.4 mm.

2n

= 120.

Bothriochloa alta

Poaceae subfam. Panicoideae

Distribution
from FNA
NM; TX
[BONAP county map]
Discussion

Bothriochloa alta grows along roads, drainage ways, and gravelly slopes in the desert grasslands of the south-western United States, at 600-1200 m, and extends south to Bolivia and Argentina. It is not a common species in the Flora region. It often grows with and is mistaken for B. barbinodis, but differs from that species in having longer culms, panicles, and nodal hairs, and 2n = 120. Plants in the southwestern United States have larger spikelets and more hairy panicles than those of central Mexico, where the species was originally described.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The subfamily Panicoideae is most abundant in tropical and subtropical regions, particularly mesic portions of such regions, but several species grow in temperate regions of the world. Within the Flora region, the Panicoideae are represented by 59 genera and 364 species. They are most abundant in the eastern United States (Barkworth and Capels 2000). Photosynthesis may be either C3 or C4. All three pathways are found in the subfamily, but the PCK and NAD-ME variants appear to have evolved only once, while the NADP-ME pathways seems to have evolved several different times (Giussani et al. 2001).

The Panicoideae were first recognized as a distinct unit by Brown (1814), earlier than any of the other subfamilial taxa of the Poaceae. Its early recognition is undoubtedly attributable to its distinctive spikelets. Recognition of the tribe Gynerieae is recent (Sanchez-Ken and Clark 2001) and its placement in the Panicoideae, rather than the Centothecoideae, should be regarded as tentative.

Spikelets with two florets are found in many other subfamilies, but rarely do they follow the pattern of the lower floret being sterile or staminate and the upper floret bisexual. Development of unisexual florets within the Panicoideae appears to be consistent across the subfamily (LeRoux and Kellogg 1999), but differs from that in the Ehrhartoideae (Zaitcheck et al. 2000).

The Paniceae and Andropogoneae have their conventional interpretation in this Flora, so far as the North American taxa are concerned. Molecular studies, however, while strongly supporting the monophyly of the Andropogoneae, show the Paniceae to be paraphyletic, with two distinct clades. In one of these clades, most taxa have a chromosome base number of x = 9, but some have x = 10, and the taxa are pan-tropical in origin. The taxa in the other clade, with one exception, have a chromosome base number of x = 10 and are American in origin. This latter clade is sister to the Andropogoneae, which also have a chromosome base number of x = 10 (Gomez-Martinez and Culham 2000; Giussanni et al. 2001; Barber et al. 2002).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Blades of leaves on the lower 1/2 of the culms disarticulating from the sheaths; plants 2-15 m tall, unisexual, without axillary inflorescences; blades with midribs 5-15 mm wide
Gynerieae
1. Blades of most or all cauline leaves remaining attached to the sheaths; plants 0.05-6 m tall, usually bisexual, sometimes with unisexual inflorescences, often with axillary inflorescences; blades with midribs 0.2-5 mm wide.
→ 2
2. Glumes usually conspicuously unequal; lower glumes usually greatly exceeded by the upper florets; upper glumes from subequal to longer than the distal florets; lemmas of the upper florets usually coriaceous to indurate; disarticulation usually beneath the glumes, not in the axes of the inflorescence branches
Paniceae
2. Glumes usually subequal, usually exceeding and concealing the florets; lemmas of the upper florets hyaline to membranous; disarticulation frequently in the axes of the inflorescence branches
Andropogoneae
Source FNA vol. 25, p. 642. FNA vol. 25, p. 351.
Parent taxa Poaceae > subfam. Panicoideae > tribe Andropogoneae > Bothriochloa Poaceae
Sibling taxa
B. barbinodis, B. bladhii, B. edwardsiana, B. exaristata, B. hybrida, B. ischaemum, B. laguroides, B. longipaniculata, B. pertusa, B. springfieldii, B. wrightii
Subordinate taxa
Andropogoneae, Gynerieae, Paniceae
Name authority (Hitchc.) Henrard Link
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