Monographs Details: Lasianthaea helianthoides DC.
Authority: Becker, Kenneth M. 1979. A monograph of the genus Lasianthaea (Asteraceae). Mem. New York Bot. Gard. 31 (2): 1-64.
Description:Species Description - Shrubs or more commonly half-shrubs woody near base only, 0.3-4 m high; young branches sordid-hirsute to viscid-pubescent. Leaves all opposite; pedole (2-)3-15 mm long, hispid to occasionally viscid-pubescent; blade thick, firm, often rugose, usually ovate to lance-ovate, varying to lanceolate and suborbicular, (3-)4-9.5(-12) cm long, 2-6(-9) cm wide, obtuse to acute or occasionally short-acuminate, cuneate to cordate at base, scabrous to viscid above, pilose to hirsute below, margin denticulate-mucronulate to serrate, occasionally slightly revolute, tripHnerved or occasionally trinerved. Inflorescence (1-)3-5-headed, terminal and from upper leaf axils. Peduncles 0.1-4 cm long, stout, white- or sordid-hirsute; heads 2-4 cm wide across extended rays. Involucre campanulate to hemispherical, 1.0-1.6 cm high, 0.6-2.5 cm wide, phyllaries graduated in 3-6 series. Outer phyllaries firm, membranous-indurate below, more or less herbaceous above, broadly ovate to ovate in outHne, 5-10 mm long, 2-8 mm wide, acute to usually obtuse, white-hirsute and puberulent dorsally, middle phyHaries often 3-lobed, inner phyllaries ovate-oblong to elliptic, 7-20 mm long, 1.5-5.6 mm wide, obtuse, often amphated at apex. Rays 8-13(-21), orange-yellow or yellow, lamina 3-20 mm long, 4-9 mm wide, tube 4-6.5 mm long. Disc florets 10-100(-125), orange or yellow, 8-15 mm long, throat narrowly campanulate to campanulate, 4.5-13 mm long, 1.5-4.5 mm wide, lobes 0.9-1.9 mm long. Anther thecae dark brown or brown, 2.5-4.0 mm long, appendage 0.6-1.5 mm long. Style branches 2.1-4.5 mm long, appendage 0.5-1.5 mm long. Pales 0.7-1.5 mm long, 0.5-1.8 mm wide as folded. Disc achenes cuneate, 2-awned, body 3-6.5 mm long, 1-4 mm wide, glabrate to puberulent, awns 4-7.5 mm long, pappus squamellae 1-2.7 mm long, usually connate. Ray achenes 3-awned, body 3.5-6 mm long, 2-4 mm wide, awns 1.5-5 m m long, pappus squamellae 1-3.2 mm long. Receptacle flat to low convex.
Zexmenia helianthoides (DC.) A. Gray, PI. Wright. 1: 113, 1852 (not Z. helianthoides (HBK.) Benth. & Hook. = Wedelia helianthoides HBK.). Type: MEXICO: Between Saltepec and Cuito, Karwinskis.n. (holotype: M; photos: MICH, NY, US).
Tithonia ovata Hook., Bot. Mag. t. 3901, 1841. Zexmenia ovata (Hook.) Benth. & Hook, f., Gen. 2: 373, 1873. Type: MEXICO: cultivated in Hort. Kew (holotype: K(herb. Hook.); photo: GH).
Lasianthaea helianthoides, the type species of the genus, is most closely related to L. macrocephala and L. crocea. As recognized here, L. helianthoides consists of two varieties, var. helianthoides, c o m m o n in the Balsas Depression of southern Mexico, and the relatively small-headed var. nayaritense, apparently restricted to northern Nayarit (Map 3). Both varieties are relatively constant morphologically within their respective ranges. The hiatus in range in Jalisco is of interest.
Lasianthaea helianthoides and L. crocea are often found growing together throughout the Balsas Depression. The major isolating mechanism between them apparently is pollinator differentiation (rays orange-yellow in L. helianthoides, orange-red to purplish in L. crocea). This mechanism apparently breaks down often enough so that they hybridize fairly freely (evidence is presented in the discussion of L. crocea below).
Lasianthaea helianthoides var. helianthoides and L. ceanothifolia var. ceanothifolia apparently hybridize on occasion. Paray 1605, from Tepoztlan, Morelos, where both species occur, is intermediate between the two in size and number of heads, and in leaf shape, texture, and pubescence. Paray 1705, from the same area, is also intermediate but shows a somewhat different assortment of characters. The hybrid nature of these collections is supported by pollen stainability data (Paray 1605: 69 1/2; Paray 1705:12 1/2; putative parents: 96 + 1/2).
For discussion of the relationship of L. helianthoides with L. squarrosa, see under the latter.