10.09 PIPTOCHAETIUM J. Presl
Mary E. Barkworth
Plants perennial; cespitose, not rhizomatous. Culms 4–150 cm, usually erect, sometimes decumbent, glabrous, not branched above the base; basal branching intravaginal; prophylls shorter than the sheaths, mostly glabrous, keels usually with hairs, apices bifid, teeth 1–3 mm; cleistogenes not developed. Sheaths open to the base, margins glabrous; ligules membranous, decurrent, truncate to acute, sometimes highest at the sides, sometimes ciliate; blades convolute to flat, translucent between the veins, often sinuous distally. Inflorescences terminal panicles, open or contracted, spikelets usually confined to the distal 1/2 of each branch. Spikelets 4–22 mm, with 1 floret; rachillas not prolonged beyond the base of the floret; disarticulation above the glumes, beneath the floret. Glumes subequal, longer than the floret, lanceolate, 3–7(8)-veined; florets globose to fusiform, terete to laterally compressed; calluses well developed, sharp or blunt, glabrous or antrorsely strigose, hairs yellow to golden brown; lemmas coriaceous to indurate, glabrous or pubescent, striate, particularly near the base, smooth, papillose, or tuberculate, often smooth on the lower portion and papillate to tuberculate distally, margins involute, fitting into the grooved palea, apices fused into a crown, awned, lemmas often narrowed below the crown, crowns usually ciliate; awns caducous to persistent, usually twice-geniculate, first 2 segments usually twisted and hispid, terminal segment straight and scabridulous; paleas longer than the lemmas, similar in texture, glabrous, sulcate between the veins, apices prow-tipped; lodicules 2 or 3, membranous, glabrous, blunt or acute; anthers 3; ovaries glabrous; styles 2. Caryopses terete to globose or lens-shaped. x = 11. Name from the Greek pipto, ‘fall’, and chaite, ‘long hair’.
Piptochaetium is primarily South American, being particularly abundant in Argentina. It has 27 species. Four species are native in the Flora region; two South American species are established at a single location in Marin County, California.
All stipoid species with elongate florets were included in Stipa by Hitchcock (1935, 1951) and other North American taxonomists. Parodi (1944) argued that Piptochaetium should be expanded to include those species of Stipa with elongated florets that shared with Piptochaetium its distinctive lemma and palea morphology, hair color, and leaf anatomy. His interpretation is now universally accepted.
The basal chromosome number of Piptochaetium is probably 11. This interpretation implies that counts of 2n = 42 (Gould 1965 and Reeder 1968 for P. fimbriatum; Reeder 1977 for P. pringlei) represent an aneuploid reduction from 2n = 44. It is also possible that the base number is 7, as is common in the Poöideae.
SELECTED REFERENCES Cialdella, A.M. and M.O. Arriaga. 1998. Revisión de las especies sudamericanas del género Piptochaetium (Poaceae, Poöideae, Stipeae). Darwinia 36:105–157; Cialdella, A.M. and L.M. Giussani. 2002. Phylogenetic relations of the genus Piptochaetium (Poaceae: Poöideae, Stipeae): Evidence from morphological data. Ann. Missouri Bot. Gard. 89:305–336; Gould, F.W. 1958. Chromosome numbers in southwestern grasses. Amer. J. Bot. 45:757–767; Gould, F.W. 1965. Chromosome numbers in some Mexican grasses. Bol. Soc. Bot. México 29:49–62; Hitchcock, A.S. 1935. Manual of the Grasses of the United States. U.S. Government Printing Office, Washington, D.C., U.S.A. 1040 pp.; Hitchcock, A.S. 1951. Manual of the Grasses of the United States, ed. 2, rev. A. Chase. U.S.D.A. Miscellaneous Publication No. 200. U.S. Government Printing Office, Washington, D.C., U.S.A. 1051 pp.; Parodi, L. 1944. Revisión de las gramíneas australes americanas del género Piptochaetium. Revista Mus. La Plata 6:213–310; Reeder, J.R. 1968. Notes on Mexican grasses VIII: Miscellaneous chromosome numbers–2. Bull. Torrey Bot. Club 95:69–86; Reeder, J.R. 1977. Chromosome numbers in western grasses. Amer J. Bot. 64:102–110; Thomasson, J.R. 1979. Late Cenozoic Grasses and Other Angiosperms from Kansas, Nebraska, and Colorado: Biostratigraphy and Relationships to Living Taxa. Kansas Geological Survey, Bulletin No. 218. University of Kansas Publications, Lawrence, Kansas, U.S.A. 68 pp.
For an interactive dichotomous key, click here; the interactive, multientry key is not yet available..
1. Florets 6.5–22 mm long; culms 40–130 cm tall ... 2
1. Florets 2.3–5.5 mm long; culms 20–95 cm tall ... 4
2. Lemmas hairy; awns 19–35 mm long ... P. pringlei
2. Lemmas glabrous; awns 40–120 mm long ... 3
3. Florets 7–13 mm long; awns 40–75 mm long ... P. avenaceum
3. Florets 13.5–22 mm long; awns 62–120 mm long ... P. avenacioides
4. Lemmas golden brown, hairy, the hairs easily rubbed off ... P. fimbriatum
4. Lemmas dark brown, glabrous ... 5
5. Awns 10–16 mm long; blades 0.8–1.5 mm wide; distal margin of the lemma crowns straight ... P. setosum
5. Awns 15–25 mm long; blades 0.2–0.4 mm wide; distal margin of the lemma crowns sometimes slightly to strongly revolute ... P. stipoides
1. Piptochaetium pringlei (Beal) Parodi
Culms 50–125 cm, mostly glabrous, pubescent below the nodes; nodes 2–3, dark, glabrous or slightly pubescent. Sheaths smooth to scabrid-ulous; ligules of basal leaves 0.5–2.8 mm, truncate to rounded, of upper leaves 1–3.5 mm, rounded to acute; blades 10–30 cm long, 1–3.5 mm wide, 3–5-veined, abaxial surfaces glabrous, smooth, adaxial surfaces smooth or scabrous over the veins, margins smooth or scabrous. Panicles 6–20 cm, open, with 10–25 spikelets; branches ascending, flexuous; pedicels to 1 mm, flattened, hispid. Glumes subequal, 9–12 mm long, 2.5–3.5 mm wide; lower glumes 5–7-veined; upper glumes 7-veined; florets 6.5–10 mm long, 1.5–2.1 mm thick, terete to somewhat laterally compressed; calluses 0.6–1.9 mm, blunt to acute, strigose; lemmas golden brown to dark brown at maturity, shiny or not, smooth to spiny-tuberculate distally or for almost their entire length, pubescent, hairs tawny to golden brown, evenly distributed or somewhat more abundant on the basal 1/2, apices tapering to the crown; crowns 0.5–0.6 mm, inconspicuous, straight, hairy, hairs 0.5–1 mm; awns 19–27(35) mm, persistent, twice-geniculate, sometimes inconspicuously so; paleas 6.3–9.5 mm; lodicules 2, 1–1.5 mm, acute; anthers 3.5–5.5 mm, sometimes penicillate. Caryopses about 7 mm, fusiform. 2n = 42.
Piptochaetium pringlei grows in oak woodlands, often on rocky soils, in the southwestern United States and northwestern Mexico. It is often confused with P. fimbriatum; it differs from that species in having longer florets and sharper calluses.
2. Piptochaetium avenaceum (L.) Parodi
Culms (30)40–100 cm, glabrous; nodes 2–3, narrowed, yellowish to reddish. Sheaths glabrous; ligules rounded, sometimes highest at the sides, entire, of basal leaves 0.4–3.3 mm, of upper leaves 1.8–2.5 mm; blades 8–30 cm long, 0.6–3 mm wide, usually involute and about 0.5 mm in diameter, 3-veined, abaxial surfaces glabrous, smooth, adaxial surfaces scabrous over the veins, margins scabrous. Panicles 14–22 cm, open, with (10)15–25 spikelets; branches lax, divergent, spikelets confined to the distal 1/2; pedicels 15–50 mm, flattened, hispid. Glumes subequal, 9–15 mm long, 0.9–1.9 mm wide, acute; lower glumes 3(5)-veined; upper glumes 5-veined; florets 7–13 mm long, 1–1.2 mm thick, terete; calluses 2–3 mm, sharp, strigose, hairs golden brown at maturity; lemmas glabrous, tan to brown at maturity, smooth below, sharply tuberculate in the distal 1/3, constricted below the crown; crowns 0.5–0.6 mm wide, straight, not revolute, hairy, hairs 0.2–0.5 mm, golden brown; awns 40–75 mm, persistent, twice-geniculate, basal segment hispid, terminal segment scabrous; paleas 7–14 mm; anthers 0.3–0.5 mm or 3–4 mm, not penicillate. Caryopses 3.5–6 mm, terete. 2n = 22. Cialdella & Giussani (2002) mistakenly cited Gould (1958) as having reported 2n = 28.
Piptochaetium avenaceum grows in open oak and pine woods, often on sandy soils, throughout most of the coastal plain of the eastern United States, extending north up the Mississippi valley, and also on the east side of Lake Michigan. With the exception of one record from southern Ontario, Canada (collected in 1965 and not seen in Canada since, even though it has been searched for, fide Michael Oldham, pers. comm.), P. avenaceum is known only from the contiguous United States.
Piptochaetium avenaceum is very similar to P. avenacioides, differing only in its smaller size and more widespread distribution. It is also similar to P. leianthum (Hitchc.) Beetle, a species of northeastern Mexico, from which it differs in its larger size. The existence of two ranges of anther length suggests that the species is sometimes cleistogamous.
3. Piptochaetium avenacioides (Nash) Valencia & Costas
Culms 70–130 cm, mostly glabrous, sometimes pubescent below the nodes; nodes yellow-ish, glabrous. Sheaths glabrous; ligules blunt to acute, of basal leaves 0.4–0.7 mm, of upper leaves to 3 mm; blades 15–30 cm long, 0.8–1.5 mm wide, usually involute and 0.5 mm in diameter, 3-veined, abaxial surfaces usually glabrous and smooth, sometimes scabrous, adaxial surfaces usually scabrous over the veins, sometimes smooth, sometimes hairy. Panicles 10–31 cm, open, with 10–50 spikelets; pedicels 15–20 mm, scabrous. Glumes 15–22 mm, (3)5-veined; florets 13.5–22 mm long, 1–2 mm thick, terete; calluses 3.5–8 mm, sharp, strigose, hairs golden brown at maturity; lemmas glabrous, tan to brown at maturity, mostly smooth, sharply tuberculate distally, contracted below the crown; crowns 0.6–0.7 mm wide, hairy, hairs 0.2–0.6 mm; awns 62–120 mm, persistent, twice-geniculate; paleas 9–12 mm; lodicules 2; anthers 4–7 mm. 2n = unknown.
Piptochaetium avenacioides grows in dry woods, generally on sandy ridges. It is endemic to Florida, growing primarily in the central peninsula. Morphologically, it is very similar to P. avenaceum, differing only in its larger size and more restricted distribution.
4. Piptochaetium fimbriatum (Kunth) Hitchc.
Culms 35–95 cm, usually glabrous, sometimes pubescent below the nodes; nodes 2–3, often dark, glabrous. Sheaths glabrous, smooth; ligules trun-cate to rounded, of basal leaves 0.4–1.8 mm, of upper leaves 1.5–2 mm; blades 6–26 cm long, usually involute and 0.3–5 mm in diameter, sometimes flat and 0.5–1(1.5) mm wide, 3-veined, both surfaces glabrous, veins often scabridulous, margins scabrous. Panicles 6.5–25 cm, open, often partially enclosed in the upper leaf sheath, with 20–60 spikelets; branches flexuous; pedicels 4–12 mm, flattened, hispid. Glumes subequal, 4–6.2 mm long, 1.8–3.1 mm wide, 5–7-veined, often partly purplish; florets 3–5.5 mm long, 0.6–1.9 mm thick, somewhat laterally compressed, rectangular to slightly obovate in side view; calluses 0.2–0.7 mm, blunt, strigose; lemmas tan to light chocolate brown, shiny, smooth, evenly pubescent when immature, hairs easily rubbed off; crowns about 0.8 mm wide, inconspicuous, glabrous or glabrate; awns 11–20 mm, persistent, twice-geniculate; paleas about 3.5 mm; lodicules 2, about 1 mm; anthers 0.3–0.5 mm, not penicillate. Caryopses 2.5–3 mm long, about 0.6 mm thick, fusiform. 2n = 42.
Piptochaetium fimbriatum is an attractive species that grows in oak and pinyon woods of the southwestern United States and adjacent Mexico, and merits consideration as an ornamental. It has also been reported from Guatemala; the report has not been verified.
Piptochaetium fimbriatum is not easily confused with other species in our range. Hitchcock (1951) treated it as including P. seleri (Pilg.) Henrard, a Mexican species with dull, rough, oblanceolate lemmas and persistent lemma hairs, an interpretation that is no longer accepted. It is occasionally confused with P. pringlei; it differs from that species in having shorter florets and blunt calluses.
5. Piptochaetium setosum (Trin.) Arechav.
Culms 20–40 cm, prostrate to ascending; nodes 2, dark, glab-rous. Sheaths glabrous, smooth; ligules 0.5–2.5 mm, obtuse, membranous, glabrous; blades (3)5–12.5 cm long, 0.8–1.5 mm wide, glabrous or hispidulous, margins scabridulous. Panicles 3–15 cm long, 2–3 cm wide, with (5)10–30 spikelets; branches appressed to ascending, glabrous or hispid; pedicels 2–6 mm, hispidulous. Glumes subequal, 5–7 mm long, 1–2 mm wide, purplish at the base; lower glumes (3)5(7)-veined; upper glumes 5(7)-veined; florets 2.5–3 mm long, 1.2–1.8 mm thick, globose to slightly laterally compressed, gibbous; calluses 0.2–0.5 mm, obtuse, antrorsely strigose, hairs whitish to golden; lemmas glabrous, longitudinally striate, constricted below the crown, chestnut brown at maturity; crowns 0.5–0.8 mm wide, straight, not strongly differentiated, distal margins papillose; awns 10–16 mm, once- or twice-geniculate; paleas to 3.2 mm; anthers about 0.5 mm. Caryopses 2–2.5 mm, spherical to ellipsoid. 2n = unknown.
Piptochaetium setosum is native to central Chile. There is an established population in Marin County, California, that grows intermingled with P. stipoides, another South American species. The two species grow in the middle of a dirt track and in the adjacent meadow. The California plants of P. setosum are notable for their prostrate culms. This characteristic was not mentioned by Parodi (1944) or Cialdella and Arriaga (1998).
The origin of the California population is not known. It has been suggested that the seeds might have been brought in by birds, as the area was a bird refuge at one time.
6. Piptochaetium stipoides (Trin. & Rupr.) Hack.
Culms 20–60 cm, erect to ascending; nodes 2–4, dark, glabrous. Sheaths glabrous or hispidulous towards the collar; ligules 0.8–2 mm, glabrous, abaxial surfaces scabridulous, margins occasionally ciliate; blades (5)14–30 cm long, 0.2–0.4 mm wide, linear, glabrous or villous, margins scabridulous. Panicles 4–15 cm long, 1.5–3 cm wide, with 10–70 spikelets; branches ascending, scabridulous; pedicels 1–11 mm, hispid. Glumes subequal, 4–8.5 mm long, 1.5–2 mm wide, purple towards the base, glabrous, 5-veined, apices aristulate; florets 2.3–4(5) mm long, 0.8–2.3 mm thick, obovoid, globose to laterally compressed; calluses 0.5–0.6 mm, blunt, hairs white to golden tan; lemmas shiny, glabrous, striate, dark brown to black at maturity, wholly smooth to conspicuously verrucose or sharply papillose, at least distally, constricted below the crown; crowns well-developed, 0.6–1.6 mm wide, distal margins slightly to strongly revolute, inner surfaces densely covered with hooks and hairs; awns 15–25 mm, eccentric, twice-geniculate, tardily deciduous; paleas 2.5–5 mm; lodicules 2, linear; anthers about 0.5 mm. Caryopses 1.5–2.5 mm, spherical to ellipsoid. 2n = unknown.
Piptochaetium stipoides is native to South America. There is one known population in the Flora region, in Marin County, California, which grows with P. setosum in a meadow adjacent to an old dirt road. The origin of the population is not known; it has been suggested that the seeds might have been brought in by birds, as the area was a bird refuge at one time.
The Californian plants belong to Piptochaetium stipoides (Trin. & Rupr.) Hack. var. stipoides, which differs from the only other variety recognized by Cialdella and Arriaga (1998), P. stipoides var. echinulatum Parodi, in having lemmas that are mostly smooth as well as a less revolute crown.