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Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

POA BLUE GRASS

Robert J. Soreng


Annual, perennial herb; some ± dioecious. Stem: 0.3–12 dm. Leaf: sheath open most of length to closed (best observed on upper stem leaf); ligule thin, flexible, without a rim of hairs; blade grooved above on both sides of midvein, flat, folded, or inrolled, generally smooth or scabrous on veins, generally prow-tipped. Inflorescence: panicle-like; branches appressed to drooping. Spikelet: generally compressed, breaking between florets; glumes 2, ± equal, generally < lowest lemma, awnless; florets generally 2–6; callus indistinct, often with obvious tuft of long cobwebby hairs; lemma generally keeled to base, like glumes, awnless, veins generally 5, hairy or glabrous, upper margins thin-membranous; palea well developed, keel generally scabrous. Flower: generally bisexual, sometimes pistillate and/or staminate; fertile anthers 0.2–4.5 mm; ovary glabrous; fruit firm.
± 500 species: temperate and cool regions. (Greek: ancient name applied to various grasses, fodder plants) [Soreng 2007 FNANM 24:486–601] California is center of diversity in North America. Spikelet data recorded from lowest florets of spikelet at 25 ×.
Unabridged references: [Gillespie & Soreng 2005 Syst Bot 30:84–105; Soreng 1998 Novon 8:187–202; Soreng 1991 Syst Bot 16:507–528; Soreng 1991 Phytologia 71:340–413]

Key to Poa

1. Annual (biennial); anthers generally 0.2–1(1.8) mm; flower generally bisexual

2. Callus glabrous — upper flowers of spikelet often pistillate

3. Spikelet axis generally hidden, terminal internode < 1/2 terminal floret; anthers 0.6–1 mm; widespread ..... P. annua

3' Spikelet axis visible, terminal internode > 1/2 terminal floret; anthers 0.2–0.5 mm; especially s California Floristic Province ..... P. infirma

2' Callus with cobwebby hairs

4. Inflorescence branches appressed; leaf blade abruptly prow-tipped; lemma veins hairy ..... P. bigelovii

4' Lower inflorescence branches eventually spreading; leaf blade abruptly or slightly prow-tipped; lemma short-hairy or surface glabrous or scabrous

5. Lemma glabrous or scabrous; leaf blade abruptly prow-tipped; some spikelet internodes > 1 mm ..... P. bolanderi

5' Lemma short-hairy; leaf blade tapered, slightly prow-tipped; spikelet internodes generally < 1 mm ..... P. howellii

1' Perennial herb; anthers often > 1.2 mm; flowers occasionally unisexual

6. Rhizomes or stolons present; anthers 1–4 mm

7. Stem and nodes distinctly compressed, keeled, wiry; leaf sheath open nearly to base; inflorescence branches scabrous ..... P. compressa

7' Stem and nodes little or not compressed or wiry; leaf sheath sometimes not open as far; inflorescence branches sometimes smooth

8. Lemma glabrous or minutely scabrous; callus long-cobwebby

9. Sheaths of upper stem leaves open most of their length; leaf blade generally flat; upper surface glabrous or sparsely scabrous; flowers bisexual ..... P. kelloggii

9' Sheaths of upper stem leaves open 1/3–7/10 their length; leaf blade flat, folded, or inrolled, upper surface sometimes finely hairy; flowers generally unisexual

10. Leaf blades thin, soft, generally 0.8–1.5 mm wide, folded, or up to 2.5 mm wide and flat; stem leaves gradually reduced in length upward; lemma (3.2)4.25–5 mm; plants with bisexual flowers or some (rarely all) pistillate or staminate ..... P. diaboli

10' Leaf blades ± thick, firm, generally 1.5–3 mm wide, never flat; stem leaves strongly reduced in length upward; lemma generally 4–7 mm; plants nearly all pistillate- or staminate-flowered ..... P. piperi

8' Lemma hairy at least on keel or callus glabrous

11. Lemma generally < 3.5 mm, lemma and callus smooth, glabrous; stem nodes generally hidden in basal tuft; inflorescence < 8 cm, branches appressed, generally smooth; flowers unisexual ..... P. atropurpurea

11' Lemma generally > 3.5 mm or ± scabrous or hairy (if < 4 mm and smooth and glabrous, then some stem nodes well exposed and inflorescence > 8 cm); inflorescence 2–30 cm, branches sometimes ± spreading, sometimes scabrous; flowers bisexual and/or unisexual

12. Leaf blade ± firm, inrolled, upper surface generally densely and finely hairy or scabrous; flowers generally unisexual (except Poa confinis); coastal dunes

13. Lemma <= 4.5 mm, glabrous to sparsely hairy; plant <= 30 cm; inflorescence ± open ..... P. confinis

13' Lemma >> 4.5 mm, glabrous to densely hairy; plant sometimes > 30 cm; inflorescence dense, branches appressed

14. Upper glume < 7 mm; lowest lemma <= 7.5 mm; stem very scabrous or coarsely hairy below inflorescence; s North Coast, Central Coast, n Channel Islands ..... P. douglasii

14' Upper glume > 7 mm; lowest lemma > 7.5 mm; stem smooth below inflorescence; n&c North Coast ..... P. macrantha

12' Leaf blade generally not firm or inrolled, upper surface glabrous or sparsely soft-hairy; flowers bisexual and/or unisexual; widespread, generally montane, rarely on coastal dunes

15. Sheath of upper stem-leaf closed nearly to top, blade > sheath ..... P. sierrae

15' Sheath of upper stem-leaf open at least 1/4 length, blade <= sheath

16. Callus glabrous (rarely short-cobwebby); lemma glabrous or hairy; flowers often pistillate

17. Lemma generally < 3.5 mm, sometimes glabrous; inflorescence linear in outline, short-branched, interrupted, many-flowered; upper stem-leaf blade > 1/5 sheath length; flowers appearing bisexual but anthers generally sterile; tall leafy-stemmed plants of moist, low-elevation meadows ..... P. pratensis × P. secunda (see Poa secunda subsp. juncifolia)

17' Lemma generally > 3.5 mm; inflorescence lanceolate to ovate in outline (otherwise sometimes as above); upper stem-leaf blade sometimes < 1/6 sheath length; flowers generally pistillate (anthers minute); cespitose or tall plants of well drained soils of slopes of forests

18. Stem-leaf blades strongly reduced upward, uppermost < 1/8 sheath length; lemma keel and marginal veins clearly hairy; plant densely cespitose (see 31. for subspecies) ..... P. fendleriana (2)

18' Stem-leaf blades generally longest at middle of stem, uppermost generally > 1/5 sheath length; lemma glabrous to sparsely scabrous or keel and marginal veins sparsely hairy; plant loosely tufted ..... P. wheeleri

16' Callus long-cobwebby (hairs > 1/2 lemma length); lemma keel and marginal veins hairy, glabrous between veins; flowers bisexual (except Poa rhizomata)

19. Sheath generally open > 3/4 length; stolons generally present; stem sometimes branching above base; lemma sometimes hairy only on keel

20. First glume generally 3-veined, not arched; lemma obviously hairy on keel and marginal veins ..... P. palustris (2)

20' First glume 1-veined, ± sickle-shaped; lemma sparsely hairy on keel and rarely on marginal veins ..... P. trivialis (2)

19' Sheath open <= 3/4 length; plant with obvious rhizomes; stem not branching above base

21. Plant often forming a dense sod; ligule truncate to rounded; inflorescence densely flowered, branches at lower nodes generally 4+ (some may be small); lemma generally < 4 mm; flowers rarely pistillate ..... P. pratensis subsp. pratensis

21' Plant not sod-forming; ligule acute; inflorescence sparsely flowered, branches at lower nodes generally 1–2; lemma generally > 4 mm; flowers occasionally pistillate ..... P. rhizomata

6' Rhizomes and stolons 0; anthers 0.2–4.5 mm

22. Stem base ± bulbous; most spikelets producing leafy bulblets or not ..... P. bulbosa

23. Spikelets not producing leafy bulblets ..... [subsp. bulbosa]]

23' Spikelets generally producing leafy bulblets ..... subsp. vivipara

22' Stem base not bulbous; florets not mostly replaced by bulblets

24. Callus cobwebby; lemma glabrous ..... P. abbreviata subsp. marshii

24' Callus glabrous, with a ring of short hairs, or cobbwebby; if callus cobbwebby then lemma also hairy to some degree

25. Callus ± cobwebby; lemma hairy on keel and generally on marginal veins but not between veins

26. Inflorescence < 10 cm, sparse or dense; plant densely cespitose

27. Plant << 20 cm; sheaths open > 3/4 length; flower generally bisexual, anthers generally 0.7–1.2 mm ..... P. abbreviata subsp. pattersonii

27' Plant > 20 cm; sheaths open <= 1/2 length; flowers pistillate, anthers vestigial ..... P. cusickii subsp. purpurascens (2)

26' Inflorescence generally > 10 cm or open; plant loosely cespitose

28. Lower glume generally 3-veined; sheaths open 3/4 length or more

29. Ligule of upper stem-leaf truncate, generally < 0.5 mm ..... P. nemoralis

29' Ligule of upper stem-leaf acute to rounded, generally > 1 mm ..... P. palustris (2)

28' Lower glume generally 1-veined; sheaths open to 3/4 length

30. Anthers <= 1 mm; inflorescence branches with flowers in top 1/3; high montane to alpine ..... P. leptocoma subsp. leptocoma

30' Anthers > 1.3 mm; some inflorescence branches with flowers from mid-length; low elevation ..... P. trivialis (2)

25' Callus glabrous or not cobwebby (ring of short callus hairs present in some Poa secunda, Poa unilateralis); lemma often hairy between veins

31. Lemma obviously hairy at least on keel and marginal veins; flowers unisexual; sheath open ± 1/3 length; uppermost stem-leaf blade firm, often highly reduced; callus glabrous ..... P. fendleriana (2)

32. Ligule 0.2–1.5 mm, margin scabrous or short-ciliate ..... subsp. fendleriana

32' Ligule 1–18 mm, margins smooth, glabrous ..... subsp. longiligula

31' Lemma often glabrous (if obviously hairy on keel and marginal veins or between, then flowers bisexual, sheaths open > 3/4 or < 1/2 length; uppermost stem-leaf blade often thin and withering or not highly reduced); callus sometimes with a crown of short hairs

33. Spikelet lanceolate to narrowly ovate in outline, little compressed; lemma weakly keeled; sheath open > 3/4 length; flowers bisexual

34. Inflorescence branches widely spreading in flower and fruit, generally densely scabrous; ligule 0.5–1.5(2.5) mm, truncate to obtuse (rarely acute), scabrous; plant delicate, spring-active; often on serpentine ..... P. tenerrima

34' Inflorescence branches generally ascending to appressed in fruit (generally spreading only in flower), ± scabrous; plant generally more robust, or summer-active, of high elevation, or delicate with branches ± smooth and ligules longer and ± smooth; on various substrates ..... P. secunda

35. Lemma glabrous (sometimes scabrous, rarely sparsely short-hairy); ligule of sterile shoots and often stem < 2 mm, ± truncate, scabrous; leaf blade ± firm, retaining shape; inflorescence branches appressed ..... subsp. juncifolia

35' Lemma ± evenly short-hairy on keel and sides across base; ligule of sterile shoots and stem generally > 2 mm, acute or acuminate, smooth or sparsely scabrous; leaf blade generally ± soft, soon withering; inflorescence branches appressed or spreading ..... subsp. secunda

33' Spikelet ± ovate in outline, obviously compressed; lemma obviously keeled to base; sheaths sometimes open < 3/4 length; flowers sometimes unisexual

36. Uppermost sheath open <= 1/2 length; lemma > 4.5 mm, sparsely hairy on keel, base, and sometimes marginal veins; flowers pistillate ..... P. cusickii subsp. purpurascens (2)

36' Uppermost sheath generally open > 1/2 length; lemma generally < 4.5 mm or glabrous (if hairy, sheath open > 3/4 length, flowers bisexual)

37. Lemma obviously hairy, < 3.6 mm; subalpine or higher ..... P. glauca subsp. rupicola

37' Lemma often glabrous, length various (if lemma obviously hairy, plant coastal)

38. Sheath open ± 9/10 length; flowers bisexual; low salty places; coast or w California

39. Inflorescence branches ascending, very scabrous, with spikelets only in top 1/2; near hot springs, Outer North Coast Ranges, Napa Co. ..... P. napensis

39' Inflorescence branches appressed, smooth to sparsely scabrous, with spikelets from near base; sea bluffs, North Coast, n&c Central Coast ..... P. unilateralis subsp. unilateralis

38' Sheath open < 9/10 length; flowers sometimes unisexual; generally ± salt-free places; montane or Great Basin Floristic Province

40. Plant generally < 1 dm; longest anthers 0.2–2 mm; upper glume generally >= first lemma; lemma sometimes sparsely short-hairy; flowers bisexual

41. Leaf firm; lemma 3–5 mm; anthers 0.7–1.8 mm ..... P. keckii

41' Leaf soft; lemma <= 3 mm; anthers 0.2–0.7 mm ..... P. lettermanii

40' Plant generally 1–7 dm; longest fertile anthers 2–4.5 mm; upper glume generally < first lemma; lemma glabrous; flowers sometimes unisexual

42. Ligule of uppermost leaf of sterile stems 2.5–6 mm, acute, smooth; lemma <= 5.5 mm; lowest true leaves lacking blades; flowers bisexual or pistillate (rarely staminate); High Sierra Nevada ..... P. stebbinsii

42' Ligule of uppermost leaf of sterile stems generally < 2 mm (if 2–3 mm, lemma > 5.5 mm), truncate to obtuse, scabrous; lowest true leaves sometimes with blades; all flowers generally unisexual; more widespread

43. Plant generally < 30 cm, base often decumbent; leaf blades of sterile stems generally > 1.5 mm wide, arched, their ligules sometimes > 2 mm; upper glume sometimes = first lemma; Klamath Ranges, High Cascade Range, n High Sierra Nevada ..... P. pringlei

43' Plant 25–70 cm, base rarely decumbent; leaf blades of sterile stems < 1.5 mm wide, erect, their ligules < 2 mm; upper glume obviously < first lemma; widespread, especially Great Basin Floristic Province ..... P. cusickii (in part)

44. Basal tuft of leaves sparse; inflorescence branches ± smooth; 1–2 stem nodes exposed; flowers pistillate ..... subsp. epilis

44' Basal tuft of leaves dense; inflorescence branches obviously scabrous; 0–1 stem nodes exposed; flowers sometimes staminate (rarely bisexual)

45. Inflorescence branches slender, longest generally > 17 mm; moist sagebrush to dry montane slopes ..... subsp. cusickii

45' Inflorescence branches stout, longest generally < 15 mm; dry ± alpine ridges — uncommon in California ..... subsp. pallida

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