Poaceae tribe Stipeae
Achnatherum
needlegrass, ricegrass
annual or perennial, not woody, branches 1 to many at the upper nodes.
10-250 cm, erect, not branching at the upper nodes;
basal branching extra- or intravaginal;
prophylls shorter than the sheaths.
basally concentrated to evenly distributed;
sheaths open, margins not fused, sometimes ciliate distally, basal sheaths sometimes concealing axillary panicles (cleistogenes), sometimes wider than the blade;
collars sometimes with tufts of hair at the sides extending to the top of the sheaths;
auricles absent;
ligules scarious, often ciliate, cilia usually shorter than the base, ligules of the lower and upper cauline leaves sometimes differing in size and vestiture;
pseudopetioles absent;
blades linear to narrowly lanceolate, venation parallel, cross venation not evident, cross sections non-Kranz, without arm or fusoid cells;
epidermes of adaxial surfaces sometimes with unicellular microhairs, cells not papillate.
sometimes concentrated at the base;
sheaths open, margins often ciliate distally;
cleistogenes not present in the basal leaf sheaths;
collars sometimes with hairs on the sides;
auricles absent;
ligules hyaline to membranous, glabrous or pubescent, sometimes ciliate;
blades flat, convolute, or involute, apices acute, flexible, basal blades not overwintering, flag leaf blades more than 10 mm long.
usually terminal panicles, occasionally reduced to racemes in depauperate plants, sometimes 2-3 panicles developing from the highest cauline node.
terminal panicles, usually contracted, sometimes 2 forming at the terminal node;
branches usually straight, sometimes flexuous.
usually with 1 floret, sometimes with 2-6 florets, laterally compressed to terete;
rachillas not prolonged beyond the base of the floret in spikelets with 1 floret, prolonged beyond the base of the distal floret in spikelets with 2-6 florets, prolongation hairy, hairs 2-3 mm;
disarticulation above the glumes and beneath the florets.
usually appressed to the branches, with 1 floret;
rachillas not prolonged beyond the floret;
disarticulation above the glumes, beneath the floret.
usually exceeding the floret(s), always longer than 1/4 the length of the adjacent floret, 1-10-veined, narrowly lanceolate to ovate, hyaline or membranous, flexible;
florets usually terete, sometimes laterally or dorsally compressed;
calluses usually well-developed, rounded or blunt to sharply pointed, often antrorsely strigose;
lemmas lanceolate, rectangular, or ovate, membranous to coriaceous or indurate, 3-5-veined, veins inconspicuous, apices entire, bilobed, or bifid, awned, lemma-awn junction usually conspicuous, awns 0.3-30 cm, not branched, usually terminal and centric or eccentric, sometimes subterminal, caducous to persistent, not or once- to twice-geniculate, if geniculate, proximal segment(s) twisted, distal segment straight, flexuous, or curled, not or scarcely twisted;
lodicules 2 or 3;
anthers 1 or 3, sometimes differing in length within a floret;
ovaries glabrous throughout or pubescent distally;
styles 2(3-4)-branched.
exceeding the floret, usually lanceolate, 1-7-veined, acute to acuminate, sometimes obtuse;
florets usually terete, fusiform or globose, sometimes somewhat laterally compressed;
calluses 0.1-4 mm, blunt to sharp, usually strigose;
lemmas stiffly membranous to coriaceous, smooth, usually hairy, sometimes glabrous, hairs on the lemma body to 6 mm, usually evenly distributed, hairs on the upper 74 sometimes somewhat longer than those below, not both markedly longer and more divergent, apical hairs to 7 mm, lemma margins usually not or only weakly overlapping, firmly overlapping in some species with glabrous lemmas, usually terminating in 0.05-3 mm lobes, sometimes unlobed, lobes usually membranous and flexible, sometimes thick, apices with a single, terminal, centric awn, awn-lemma junction evident;
awns 3-80 mm, centric, readily deciduous to persistent, usually scabrous to scabridulous, sometimes hairy in whole or in part, if shorter than 12 mm, usually deciduous, not or once-geniculate and scarcely twisted, if longer than 12 mm, usually persistent, once- or twice-geniculate and twisted below, terminal segment usually straight, sometimes flexuous;
paleas from 1/3 as long as to slightly longer than the lemmas, usually pubescent, 2-veined, not keeled over the veins, flat between the veins, veins usually terminating below the apices, sometimes prolonged 1-3 mm, apices usually rounded;
lodicules 2 or 3, membranous, not lobed;
anthers 3, 1.5-6 mm, sometimes penicillate;
ovaries with 2 style branches, branches fused at the base.
ovoid to fusiform, not beaked, pericarp thin;
hila linear;
embryos less than 1/3 the length of the caryopses.
fusiform, not ribbed, style bases persistent;
hila linear, almost as long as the caryopses;
embryos 1/5 – 1/3 the length of the caryopses.
= 7, 8, 10, 11, 12.
= 10 or 11.
Poaceae tribe Stipeae
Achnatherum
The tribe Stipeae includes about 15 genera and approximately 500 species. It grows in Africa, Australia, South and North America, and Eurasia. In Australia, South America, and Asia, it is often the dominant grass tribe over substantial areas. It is not present in southern India, and is represented by only one native species in southern Africa. Most species grow in arid or seasonally arid, temperate regions.
Morphological considerations have led to the Stipeae being placed in three different subfamilies (Pooideae, Bambusoideae, and Arundinoideae) in the past, and even to recognition as a subfamily. Molecular data support its treatment as an early diverging lineage within the Pooideae (Soreng and Davis 1998; Grass Phylogeny Working Group 2001) that is more closely related to the Meliceae than the core pooid tribes.
Decker (1964) suggested including Ampelodesmos in the Stipeae on the basis of the cross sectional anatomy of its leaf blades. His suggestion is supported, not always strongly, by molecular studies (Soreng and Davis 1998; Grass Phylogeny Working Group 2001; Jacobs et al. 2006). The usual alternative is to treat Ampelodesmos as the only genus of a closely related, monospecific tribe, the Ampelodesmeae (Conert) Tutin, because it is so distinct from other members of the Stipeae, being, for example, the only member of the tribe with more than 1 floret in its spikelets and rachillas that are prolonged beyond the base of the terminal floret in a spikelet.
The lowest chromosome number known in the Stipeae is 2n =18 (Prokudin et al. 1977), suggesting that all members of the tribe are ancient polyploids. The wide range of base numbers listed is based on numbers for the various genera. The primary basic chromosome number for the tribe is probably 5 or 6, with higher numbers reflecting ancient euploidy.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
As interpreted here, Achnatherum is one of the larger and more widely distributed genera in the Stipeae. It is difficult to estimate how many species it contains because its boundaries are still unclear. Of the 28 species in the Flora region, only A. splendens, from Europe, is introduced.
Most species of Achnatherum used to be included in Stipa, a genus that at one time included almost all Stipeae with an elongated floret. Keng (cited in Tsvelev 1977) transferred some Chinese species of Stipa sensu lato with blunt calluses and less indurate lemmas than Stipa sensu stricto to Achnatherum, a realignment that Tsvelev (1977) supported. Thomasson (1978) demonstrated that several North and South American species of Stipa had lemma epidermes similar to those of the Eurasian species of Stipa that had been transferred to Achnatherum. After considering various additional characters (Barkworth 1981, 1982), Barkworth (1993) transferred most North American species of Stipa and some of Oryzopsis into the expanded Achnatherum. In retrospect, her transfer of South American species to Achnatherum was ill-advised. Some have since been transferred to Amelichloa (Arriaga and Barkworth 2006), others to Jarava (Peiiailillo 2002). With its current boundaries, Achnatherum is probably still polyphyletic (Jacobs et al. 2006), but the evidence does not support return of the North American species treated as Achnatherum to either Stipa or Oryzopsis.
In the key, glume widths are the distance between the midvein and the margin. Floret lengths include the callus, but not the apical lobes. Floret thickness refers to the thickest part of the floret.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Spikelets with 2-6 florets | Ampelodesmos |
1. Spikelets with 1 floret. | → 2 |
2. Paleas sulcate, longer than the lemmas; lemma margins involute, fitting into the paleal groove; lemma apices not lobed | Piptochaetium |
2. Paleas flat, from shorter than to longer than the lemmas; lemma margins convolute or not overlapping; lemma apices often lobed or bifid. | → 3 |
3. Prophylls exceeding the leaf sheaths; plants cultivated as ornamentals. | → 4 |
4. Panicles contracted; lemma awns once-geniculate | Macrochloa |
4. Panicles open; lemma awns twice-geniculate | Celtica |
3. Prophylls concealed by the leaf sheaths; plants native, introduced, sometimes cultivated as ornamentals. | → 5 |
5. Flag leaf blades up to 12 mm long; basal leaves overwintering | Oryzopsis |
5. Flag leaf blades more than 10 mm long; basal leaves not overwintering. | → 6 |
6. Plants with multiple stiff branches from the upper nodes; pedicels sometimes plumose; species cultivated as ornamentals in the Flora region | Austrostipa |
6. Plants not branching at the upper nodes, or with a few, flexible branches; pedicels never plumose; species native, established introductions, or cultivated as ornamentals. | → 7 |
7. Apices of the leaf blades sharp and stiff; caryopses obovoid, often with 3 smooth ribs at maturity; cleistogenes usually present | Amelichloa |
7. Apices of the leaf blades acute to acuminate, never both sharp and stiff; caryopses fusiform, ovoid or obovoid, without ribs; cleistogenes sometimes present. | → 8 |
8. Lemma margins strongly overlapping their whole length at maturity, lemma bodies usually rough throughout, apices not lobed; paleas 1/4 - 1/2 the length of the lemmas, without veins, glabrous | Nassella |
8. Lemma margins usually not or only slightly overlapping for some or all of their length at maturity, strongly overlapping in some species with smooth lemmas, lemma bodies usually smooth on the lower portion, apices often 1-2-lobed; paleas from 1/3 as long as to equaling or slightly exceeding the lemmas, 2-veined at least on the lower portion, usually with hairs or both lemmas and paleas glabrous. | → 9 |
9. Calluses 1.5-6 mm long, sharply pointed; plants perennial or annual, if perennial, awns 65-500 mm long, if annual, awns 50-100 mm long; panicle branches straight. | → 10 |
10. Lower ligules densely hairy, upper ligules less densely hairy or glabrous; plants perennial | Jarava |
10. Ligules glabrous or inconspicuously pubescent, lower and upper ligules alike in vestiture; plants perennial or annual. | → 11 |
11. Plants perennial; florets 7-25 mm long; awns scabrous or pilose on the first 2 segments, the terminal segment scabrous, or if pilose, the hairs 1-3 mm long | Hesperostipa |
11. Plants annual or perennial, if annual, the florets 4-7 mm long and the awns not plumose, if perennial, the florets 18-27 mm long and the awns plumose on the terminal segment, the hairs 5-6 mm long | Stipa |
9. Calluses 0.1-2 mm long, blunt to sharply pointed; plants perennial; awns 1-70 mm; panicle branches straight or flexuous. | → 12 |
12. Florets usually dorsally compressed at maturity, sometimes terete; paleas as long as or longer than the lemmas and similar in texture and pubescence; lemma margins separate for their whole length at maturity | Piptatherum |
12. Florets terete or laterally compressed at maturity; paleas often shorter than the lemmas, sometimes less pubescent, sometimes as long as the lemmas and similar in texture and pubescence; lemma margins often overlapping for part or all of their length at maturity. | → 13 |
13. Glumes without evident venation, glume apices rounded to acute; plants subalpine to alpine, sometimes growing in bogs | Ptilagrostis |
13. Glumes with 1-3(5) evident veins or the glume apices attenuate; plants growing from near sea level to subalpine or alpine habitats, not growing in bogs. | → 14 |
14. Lemma bodies with evenly distributed hairs of similar length or completely glabrous, sometimes with longer hairs around the base of the awn; basal segment of the awns sometimes with hairs up to 2 mm long | Achnatherum |
14. Lemma bodies with hairs to 1 mm long over most of their length, with strongly divergent hairs 3-8 mm long on the distal 1/4, or the basal segment of the awns with hairs 3-8 mm long | Jarava |
1. Awns persistent, basal segments pilose, at least some hairs 0.5-8 mm long. | → 2 |
2. Flag leaves with ligules 3-8 mm long; lemmas with 1 apical lobe, the lobe to 0.1 mm long, thick, coriaceous | A. thurberianum |
2. Flag leaves with ligules 0.3-3 mm long; lemmas usually with 2 apical lobes, sometimes not lobed, lobes to 1 mm long, thin, membranous. | → 3 |
3. Basal awn segments with hairs of mixed lengths, the longer hairs scattered among the shorter hairs; apical lemma hairs longer than most basal awn hairs. | → 4 |
4. Florets 8-9 mm long; glumes 1.3-1.9 mm wide from midvein to margin | A. latiglume |
4. Florets 5-7.5 mm long; glumes 0.6-1 mm wide from midvein to margin. | → 5 |
5. Calluses 0.5-0.7 mm long; paleas 1/2 - 3/4 as long as the lemmas; palea apices with hairs usually about 1 mm long | A. nevadense |
5. Calluses 0.8-1.2 mm long; paleas z/s-/s as long as the lemmas; palea apices with hairs usually less than 1 mm long | A. occidentale |
3. Basal awn segments with hairs that gradually and regularly decrease in length distally; apical lemma hairs usually similar in length to the longest basal awn hairs, sometimes longer on the adaxial side. | → 6 |
6. Basal blades curling with age, forming circular arcs; paleas 1/4 - 1/3 as long as the lemmas; panicles 7-11 cm long | A. curvifolium |
6. Basal blades straight to lax, not forming circular arcs; paleas 2/5 – 4/5 as long as the lemmas; panicles 5-30 cm long. | → 7 |
7. Florets 5.5-7.5 mm long; paleas 2/5 – 3/5 as long as the lemmas; glumes less than 1 mm wide from midvein to margin | A. occidentale |
7. Florets 8-9 mm long; paleas 3/5 – 4/5 as long as the lemmas; glumes 1.3-1.9 mm wide from midvein to margin | A. latiglume |
1. Awns deciduous or persistent, basal segments scabrous or with hairs shorter than 0.5 mm. | → 8 |
8. Lemmas evenly hairy, hairs 1.2-6 mm long, hairs on the lemma body usually not evidently shorter than those at the apices. | → 9 |
9. Awns persistent. | → 10 |
10. Plants sterile, the anthers indehiscent, with few pollen grains (see discussion following A. hymenoides) | hybrids of 26. Achnatherum hymenoides |
10. Plants fertile, the anthers dehiscent, with many pollen grains. | → 11 |
11. Sheaths not becoming flat and ribbonlike with age; blades usually involute and 0.2-0.4 mm in diameter, 0.5-1 mm wide when flat; awns twice-geniculate | A. pinetorum |
11. Sheaths becoming flat and ribbonlike with age; blades 0.5-1.5 mm in diameter when convolute, to 7 mm wide when flat; awns once- or twice-geniculate. | → 12 |
12. Awns twice-geniculate, culms 3-6 mm thick | A. coronatum |
12. Awns once-geniculate, culms 0.8-2 mm thick | A. parishii |
9. Awns rapidly deciduous. | → 13 |
13. Florets at least 4.5 mm long, fusiform, anthers sometimes indehiscent. | → 14 |
14. Anthers dehiscent, the pollen grains well formed | A. webberi |
14. Anthers indehiscent, the pollen grains poorly formed. | → 15 |
15. Anthers dimorphic, 1 longer than the other 2; lemmas with 7 veins | see 10.11 ×Achnella |
15. Anthers all alike; lemmas with 5 veins (see discussion of hybrids on p. 142) hybrids of | A. hymenoides |
13. Florets 2.5-4.5 mm long, usually ovoid to obovoid, sometimes fusiform, anthers dehiscent. | → 16 |
16. Panicle branches terminating in a pair of spikelets on conspicuously divaricate, unequal to subequal pedicels, most shorter pedicels at least 1/2 as long as the longer pedicels | A. hymenoides |
16. Panicle branches terminating in a pair of spikelets on loosely appressed, unequal pedicels, most shorter pedicels less than 1/2 as long as the longer pedicels. | → 17 |
17. Panicles 0.5-2.8 cm wide, branches 0.5-5 cm long, strongly ascending; spikelets evenly distributed over the branches | A. arnowiae |
17. Panicles 7-15 cm wide, branches 5-8 cm long, ascending to strongly divergent; spikelets confined to the distal 1/2 of the branches | A. contractum |
8. Lemmas glabrous or with hairs 0.2-1.5(2) mm long at midlength, glabrous or with hairs distally, the hairs at midlength often evidently shorter than those at the lemma apices. | → 18 |
18. Apical lemma hairs 2-7 mm long, usually 1+ mm longer than those at midlength. | → 19 |
19. Calluses sharp; paleas 1/3-1/2 as long as the lemmas | A. scribneri |
19. Calluses blunt to acute; paleas 1/2-9/10 as long as the lemmas. | → 20 |
20. Awns twice-geniculate; culms 3-6 mm thick | A. coronatum |
20. Awns once-geniculate; culms 0.8-2 mm thick | A. parishii |
18. Apical lemma hairs absent or to 2.2 mm long, usually less than 1 mm longer than those at midlength. | → 21 |
21. Awns 5-12 mm long, readily deciduous, not or only once-geniculate. | → 22 |
22. Lemmas glabrous. | → 23 |
23. Panicles lax, the branches flexuous, diverging | A. wallowaense |
23. Panicles erect, the branches straight, ascending to appressed | A. hendersonii |
22. Lemmas pubescent. | → 24 |
24. Culms 30-250 cm long; plants cultivated ornamentals | A. splendens |
24. Culms 15-25 cm long; plants native in the Flora region | A. swallenii |
21. Awns 10-80 mm long, persistent, once- or twice-geniculate. | → 25 |
25. Terminal awn segment flexuous. | → 26 |
26. Panicles contracted, all branches straight, appressed or strongly ascending; ligules on the flag leaves to 1.5 mm long | A. aridum |
26. Panicles open, the lower branches flexuous, ascending to widely divergent; ligules on the flag leaves to 4.5 mm long | A. eminens |
25. Terminal awn segment straight or slightly arcuate. | → 27 |
27. Panicle branches flexuous, ascending to strongly divergent; spikelets pendulous | A. richardsonii |
27. Panicle branches straight, usually appressed to ascending, sometimes divergent; spikelets appressed to the branches. | → 28 |
28. Flag leaves with a densely pubescent collar, the hairs 0.5-2 mm long; paleas 2/3 - 3/4 as long as the lemmas | A. robustum |
28. Flag leaves glabrous or sparsely pubescent on the collar, the hairs shorter than 0.5 mm; paleas from 1/3 as long as to longer than the lemmas. | → 29 |
29. Lemma apices 2-lobed, lobes 1-3 mm long; palea veins extending beyond the palea body, reaching to the tips of the lemma lobes | A. stillmanii |
29. Lemma apices unlobed or with lobes to 1.2 mm long; palea veins terminating before or at the palea apices. | → 30 |
30. Apical lemma lobes thick, stiff, about 0.1 mm long; florets somewhat laterally compressed | A. lemmonii |
30. Apical lemma lobes membranous, 0.1-1.2 mm long; florets terete. | → 31 |
31. Lower cauline internodes densely pubescent for 3-9 mm below the nodes, more shortly and less densely pubescent elsewhere | A. diegoense |
31. Lower cauline internodes glabrous or slightly pubescent to 5 mm below the nodes, usually glabrous elsewhere. | → 32 |
32. Glumes subequal, the lower glumes exceeding the upper glumes by less than 1 mm. | → 33 |
33. Paleas 3/5 – 9/10 as long as the lemmas, the apical hairs exceeding the apices; blades 0.5-2 mm wide; awns 12-25 mm long | A. lettermanii |
33. Paleas 1/3 – 2/3 as long as the lemmas, the apical hairs usually not exceeding the apices; blades (0.5)1.2-5 mm wide; awns 19-45 mm long | A. nelsonii |
32. Glumes unequal, the lower glumes exceeding the upper glumes by 1-4 mm. | → 34 |
34. Apical lemma hairs erect; lemma lobes 0.5-1.2 mm long | A. lobatum |
34. Apical lemma hairs divergent to ascending; lemma lobes 0.2-0.5 mm long | A. perplexum |
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