Lactuca L.

Herbs annual, biennial or perennial with white latex; roots simple or with a stout rootstock; stems sometimes rhizomatous, very variable, erect, glabrous or hispid, pubescent or sparsely hairy, solitary or branched. Leaves very variable, radical or alternate, glabrous, pubescent or sparsely hairy, sometimes membranous and prickly, entire or dentate or variously toothed, often lobed, pinnate, pinnatifid or runcinate- pinnatifid, sessile or petioled. Inflorescence usually panicled, sometimes corymbose, umbelled or fascicled. Heads erect or drooping, narrowly cylindric; peduncle slender, naked or bracteate. Involucral bracts in one, two or three rows, differentiated into outer and inner, ovate or oblanceolate or linear-oblong; inner bracts usually longer, linear, linear-lanceolate or linear-oblong, glabrous or hispid. Florets ligulate; corolla usually yellow, sometimes blue, pinkish or purple. Stamens 5, appendaged. Style very slender; stigma bifid. Achenes variously shaped, glabrous or sparsely hairy, usually ribbed, with a prominent beak. Pappus white, simple or plumose, soft.

Cosmopolitan; ca 150 species, 24 in India.

Literature. SHIH CHU (1988). Revision of Lactuca L. and two new genera of tribe Lactuceae (Compositae) on the mainland & Asia. Act. Phytotax. Sin. 25(5): 382-393. STEBBINS, G.L. Jr. (1937). Critical Notes on Lactuca and related genera. J. Bot. 75: 12-18. STEBBINS, G.L. Jr. (1939). Notes on some Indian species of Lactuca. Ind. For. Rec. 6: 237-246. VRIES I.M. DE, & C.E. JARVISI (1986). Typification of seven Linnaean names in the genus Lactuca L. (Compositae : Lactuceae). Taxon 36: 142-154. WHrrAKER, T.w. & I.C. JAGGER (1939). Cytogenetic observation in Lactuca. Agr. Res. 58: 297-306.

The genus Lactuca comprises the following seven sections.

KEY TO THE SECTIONS

1a. Annuals or biennials; leaves chiefly radical, rarely cauline

0

b. Annual, biennial or porennial herbs; leaves radical as well as cauline

0

2a. Stems with long, straight flowering branches; achenes muricate, blackish; ligules pinkish

1. BRACHYRAMPHUS

b. Stems short with very stout flowering branches; achenes smooth, pale; ligules purplish

2. CHORISMA

3a. Branches intricate, spinescent, very slender, silvery, covered by decurrent bases of leaves

6. PHAENIXOPUS

b. Branches paniculate, without spines, slender, leaves petioled or sessile leaves

4

4a. Herbs without rootstock; heads erect, panicled; outer involucral bracts passing into the inner

5

b. Herbs with large tuberous or fusifonn roolItock; heads drooping, in large terminal panicle or paniculate racemes; outer involucral bracts small; inner bracts long

6

5a. Stems glabrous or somewhat prickly, sometimes hispid at the base; midrib prickly beneath (L. serriola); beak of achenes capillary, white

7. SCARIOLA

b. Stems glabrous, stout; leaves pungent with no prickly midrib; beak of achenes capillary, pale brown or dark brown

3. LACTUCOPSIS

6a. Leaves with broad, winged petiole, dilated or sagittately auricled at base; heads narrowly cylindric

5. MULGEDIUM

b. Leaves sessile, contracted into a cordate, auricled or 1/2 amplexicaul base; heads broadly campanulate

4. MELANOSERIS

List of Lower Taxa