treatments/MALACOTHRIX

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MALACOTHRIX de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr.. 7: 192. 1838.

Desertdandelion [Greek malakos, soft, and thrix , hair]

W. S. Davis,

Annuals or perennials, 2–70(–200) cm; taprooted (rhizomatous or taproots becoming caudices in M. saxatilis). Stems 1–15 (usually from basal rosettes), usually erect, sometimes ± prostrate, usually branched (scapiform in M. californica), usually glabrous (sometimes piloso-hirsute, stipitate-glandular, or tomentose to arachnose or puberulent, at least proximally or in leaf axils). Leaves usually basal and cauline; sessile; blades mostly oblong or lanceolate to obovate, oblanceolate, or spatulate (often pinnately lobed), ultimate margins entire or ± dentate (faces usually glabrous, sometimes piloso-hirsute or tomentose to arachnose or puberulent). Heads usually in corymbiform to paniculiform arrays (borne singly in M. californica). Peduncles not inflated distally, usually bracteate. Calyculi 0 (outer phyllaries intergrading with inner) or of 3–30+, ± deltate or lanceolate to linear or subulate, subequal to unequal bractlets (in 1–2 series distinct from phyllaries, margins usually hyaline, faces usually glabrous, sometimes arachnose, rarely stipitate-glandular). Involucres usually broadly to narrowly campanulate, sometimes hemispheric, (5–22+ ×) 2–22+ mm diam. Phyllaries either (without calyculi) 25–80+ in 4–6+ series and orbiculate to oblong, lance-oblong, lanceolate, or linear, unequal, or (with calyculi) 12–25+ in 2–3 series and oblong or lanceolate to linear, subequal; margins ± hyaline, 0.05–2.5 mm, apices obtuse to acute or acuminate. Receptacles flat to ± convex, pitted or smooth, sometimes bristly, epaleate. Florets 15–270; corollas yellow or white (sometimes reddish or lavender abaxially; outer ligules exserted 1–15 mm). Cypselae (monomorphic) stramineous to brown or purplish brown, ± prismatic or cylindro-fusiform, not beaked, ribs 15 (often 5 more prominent than others, apices of ribs sometimes projecting and forming coronas subtending pappi), usually glabrous (sometimes minutely hirtellous or muriculate); pappi 0, or (single or double) persistent, whitish, crenate crowns or rings of (1–)8–25+ teeth (mostly 0.05–0.1 mm) plus 0–6, coarse, smooth bristles (setiform scales), all in ± 1 series, subtending (i.e., exterior to) the readily falling, inner (or single and only) pappi of 15–35, basally coherent, white, fine, smooth to barbellulate or (proximally) ± plumose bristles in 1 series (falling all together or in groups). x = 7, 9.


Species 20 (18 in the flora):w United States; nw Mexico; introduced in South America.;


SELECTED REFERENCES
Davis, W. S. 1997. The systematics of annual species of Malacothrix (Asteraceae: Lactuceae) endemic to the California Islands. Madroño 44: 223–244.Williams, E. W. 1957. The genus Malacothrix (Compositae). Amer. Midl. Naturalist 58: 494–512.


1. Perennials (sometimes flowering first year). (2.)
2. Corollas medium yellow; persistent pappi 0 8. Malacothrix incana
2. Corollas white (usually each with abaxial purple stripe); persistent pappi of fimbriate crowns or 20–25, blunt teeth (0.01–0.05 mm) plus 0 bristles 12. Malacothrix saxatilis
1. Annuals. (3.)
3. Involucres hemispheric; phyllaries orbiculate (outer) to oblong or linear, hyaline margins 1–2.5 mm wide 3. Malacothrix coulteri
3. Involucres usually ± campanulate (to hemispheric in M. sonchoides ); bractlets of calyculi and/or phyllaries ovate to lanceolate, linear, or subulate, hyaline margins 0.05–0.3(–1) mm wide. (4.)
4. Stems seldom branched (heads usually borne singly on scapiform peduncles); cypsela ribs: 5 more prominent than others 1. Malacothrix californica
4. Stems branched (heads usually in corymbiform to paniculiform arrays); cypsela ribs ± equal, or 5 more prominent than others. (5.)
5. Cauline leaves not or seldom notably reduced distally (Channel Islands, California). (6.)
6. Persistent pappi usually 0, rarely of 1–2 bristles; pollen 70–100% 3-porate. (7.)
7. Stems erect or ± prostrate (forming mats); proximal cauline leaves usually fleshy (lobes nearly equal, apices obtuse); San Miguel, Santa Cruz, and Santa Rosa islands 9. Malacothrix indecora
7. Stems erect (not forming mats); proximal cauline leaves usually not fleshy (lobes usually unequal, apices acute or obtuse); Anacapa, San Clemente, San Nicolas, and Santa Barbara islands 6. Malacothrix foliosa
6. Persistent pappi of 15–20 teeth (0.01–0.1 mm) plus 1–2 bristles; pollen 70–100% 4-porate. (8.)
8. Calyculi 0; phyllaries 31–49 in 5–6+ series, hyaline margins 0.6–1 mm wide; Anacapa and Santa Cruz islands, California 16. Malacothrix squalida
8. Calyculi of 7–11 bractlets; phyllaries 9–13 in 2–3 series, hyaline margins 0.1–0.2 mm wide; Anacapa Island, California 10. Malacothrix junakii
5. Cauline leaves usually reduced distally ( M. clevelandii and M. similis are known from Channel Islands, California). (9.)
9. Corollas 4–10 mm; outer ligules exserted 1–4 mm. (10.)
10. Proximal cauline leaves (pinnately lobed, lobes 3–5 pairs, ± equal, bases white-hairy) ± fleshy; persistent pappi of crenate crowns plus 0 bristles; pollen 70–100% 3-porate 11. Malacothrix phaeocarpa
10. Proximal cauline leaves (pinnately lobed or not) not fleshy; persistent pappi of 8–24+ teeth plus 1–2 bristles; pollen 3- or 4-porate. (11.)
11. Proximal cauline leaves oblanceolate to lance-linear; corollas pale yellow; cypselae ± cylindro-fusiform or prismatic, 1.2–1.8 mm (ribs extending to apices, 5 more prominent than others); persistent pappi of 14–24+ needlelike teeth plus 1 bristle (mainly California). (12.)
12. Stems branched mostly distally, glabrous; cauline leaves: margins usually dentate; cypselae (stramineous to brown) 1.2–1.8 mm; pollen 3-porate (mean diam. 25 µm) 2. Malacothrix clevelandii
12. Stems branched mostly proximally; cauline leaves: margins usually entire; cypselae 1.4–1.7 mm (purplish brown); pollen 4-porate (mean pollen diam. 30 µm) 13. Malacothrix similis
11. Proximal cauline leaves obovate to narrowly oblanceolate; corollas white or pale yellow; cypselae ± cylindro-fusiform, 1.7–2.3 mm (ribs not extending to apices, ± equal); persistent pappi of 8–18 teeth plus 1–2 bristles (Arizona, California, Nevada). (13.)
13. Corollas white or pale yellow; cypselae 1.7–2 mm (bases slightly expanded, distal 0.3 mm smooth); pollen 70–100% 3-porate 15. Malacothrix sonorae
13. Corollas usually yellow, sometimes white; cypselae 1.7–2.3 mm (bases not expanded, distal 0.1–0.2 mm smooth); pollen 70–100% 4-porate 17. Malacothrix stebbinsii
9. Corollas (7–)10–23+ mm; outer ligules exserted 5–15+ mm. (14.)
14. Proximal cauline leaves pinnately lobed (lobes 2–6+ pairs, filiform or triangular to oblong, subequal to unequal, apices acute), not fleshy, ultimate margins dentate or entire; cypsela ribs ± equal. (15.)
15. Proximal cauline leaves usually pinnately lobed (lobes filiform); receptacles bristly; cypselae ± cylindro-fusiform (sometimes weakly 5-angled, ribs extending to apices) 7. Malacothrix glabrata
15. Proximal cauline leaves sometimes pinnately lobed (lobes relatively broad, triangular to deltate); receptacles not bristly; cypselae ± cylindro-fusiform (ribs not extending to apices, distal 0.3 mm of cypselae smooth) 4. Malacothrix fendleri
14. Proximal cauline leaves pinnately lobed (lobes 3–8 pairs, ± oblong to triangular, ± equal, apices obtuse or acute), ± fleshy, ultimate margins usually dentate; cypsela ribs ± equal or 5 more prominent than others. (16.)
16. Corollas white or yellow (usually with lavender abaxially); cypselae 1.2–2 mm; persistent pappi 0 5. Malacothrix floccifera
16. Corollas lemon or medium yellow; cypselae 1.8–4 mm; persistent pappi of 12–25+ irregular, blunt teeth plus 0–6 bristles. (17.)
17. Distal cauline leaves narrowly triangular to linear (bases usually ± dilated, ± clasping); persistent pappi of crenate crowns or 12–25+ teeth plus 0 bristles 14. Malacothrix sonchoides
17. Distal cauline leaves ± elliptic to linear (bases narrowly cuneate); persistent pappi of 12–15 teeth plus 0–6 bristles 18. Malacothrix torreyi