PARTHENIUM

Parthenium L., Sp. Pl. 2: 988. 1753; Gen. Pl. ed. 5: 426. 1754; Fl. China @ eFloras.org 20-21: 877; Strother, Fl. North Amer. @ eFloras.org 21: 20; Chowdhery in Hajra et al., Fl. India 12: 403. 1995.

Annual, biennial or perennial shrubs or subshrubs. Stem erect, usually branched. Leaves usually cauline, sometimes in rosettes; alternate, petiolate or sessile; leaf blade elliptic, lanceolate, linear, lyrate, oblanceolate, obovate, ovate, orbicular-deltate or spatulate, sometimes pinnately (1-) or 2-lobed, ultimate margins entire or toothed, faces usually hairy and gland-dotted (at least abaxial). Capitula usually radiate, sometimes +/- disciform. Involucres hemispheric; phyllaries falling, 10(-16) in 2 series, usually free, outer 5(-8) herbaceous to scarious, inner 5-8 scarious to membranous. Receptacles flat to conic; paleae cuneate to flabelliform, scarious or membranous, distally papillate and/ or fimbriate, all or the peripheral each +/- enfolding a disc floret. Ray florets: 5-8, fertile; corollas ochroleucous (off-white colour or white tinted with yellow); tube stout, glandular; limb oblong to reniform or orbiculate or +/- coroniform. Disc florets: 12-60+, functionally staminate. Corolla ochroleucous, funnelform, lobes 5. Stamens 5, filaments distinct, anthers connate. Cypselae black, oblanceoloid, obovoid or pyriform, often +/- obcompressed, shed together with subtending phyllaries and their investing paleae. Pappi 0.

19 species

Parthenium hysterophorus

Parthenium hysterophorus L., Sp. Pl. 2: 998. 1753; Rao, Bomb. Natl. Hist. Soc. 54: 218. 1956; Mathew, Fl. Tamil Carnat. 2: t. 383. 1982; Chowdhery in Hajra et al., Fl. India 12: 403.f. 113. 1995; Dhaliwal & Sharma, Fl. Kullu Dist. 389. 1999; Kaur & Sharma, Fl. Sirmaur 389. 2004; Singh & Sharma, Fl. Chamba Dist. 424. 2006; Fl. China @ eFloras.org 20-21: 877; Fl. North Amer. @ eFloras.org 21: 22

Annual herbs, 30-150 cm tall. Stem erect, much branched, longitudinally grooved, scabrid. Leaves in rosette on young plant; in mature plant leaves alternate, petiolate, petiole up to 5 cm long, slightly winged; leaf blade ovate to elliptic or deltoid, 3-18 cm x 1-5(-12) cm, pinnately or bipinnately dissected, ultimate lobes lanceolate to linear, 3-50 mm x 2-15 mm, entire or with 1 or 2 minute lobes, both surfaces sparsely to densely scaberulose and gland-dotted, occasional 1-2 mm long erect hairs. Synflorescence of open panicles, terminal or axillary. Capitula 4-5 mm across, obscurely radiate; peduncles 1-15 mm long, densely scaberulous. Involucre hemispheric; phyllaries 10-12 in 2 series: outer phyllaries 5 or 6, ovate to elliptic-lanceolate, 2-4 mm, acute, hairy on upper 2/3 portion; inner phyllaries 5 or 6, ovate, obovate to orbicular, 2.5-4 mm, transparent, subtending the ray floret (female) with one disc floret (male) on either side, the disc floret in turn enclosed by bract. Receptacle conic, paleate. Paleae nearly equal to male florets, wedge-shaped, apex fimbriate. Ray florets: 5, female, fertile. Corollas ochroleucous; tubes stout, glandular; limb reniform or orbicular to oblong, 0.3-1 mm (or corolla cup-shaped). Style short, bifid. Disc florets: 12-30(-60), present in centre, male, +/- 1.5 mm long. Corolla ochroleucous, funnelform, lobes 5. Stamens 5, filaments free, anthers connate. Cypselae obovoid, 1.5-2.5(-3.5) mm long, dark black; 5 cypselae per capitulum. Pappus of 2, lateral reflexed scales (or 2-3 pappus-like enations). Pappus like enations erect, deltate to ovate, 0.5-1 mm (sometimes a third, subulate spur near apex adaxially). Five small cypselae (achenes) usually produced per capitulum in dehiscing units; dehiscing units, 1.5-2.5 mm long, consisting of a black cypsela topped with 2 or 3 scale like pappus (ca. 0.5-1 mm long), 2 straw-colored papery structures (actually dead tubular florets), 2 paleae and a bract (inner phyllary).

Larvae and adults of Zygogramma bicolorata (Parthenium Beetle or Mexican Beetle) feed upon the leaves of Parthenium hysterophorus.

Flowering and Fruiting: Anytime of the year or commonly during the rainy season (July to September)
Common Names: Congress Grass, Carrot Grass