Flower structure in ten Asteraceae species: considerations about the importance of morpho-anatomical features at species and tribal level

Abstract

Flowers of Asteraceae have conspicuous features that are important at the tribal level, such as the branches of the style, pappus, shape of the corolla, and anthers. The floral ontogeny of ten Brazilian weed species of Asteraceae was performed for Conyza bonariensis L., Cosmos sulphureus Cav., Eclipta alba L., Elephantopus mollis Kunth, Emilia sonchifolia L. DC., Galinsoga quadriradiata Ruiz and Pav., Erechtites valerianifolius (Link ex Spreng) DC., Parthenium hysterophorus L. Praxelis clematidea R. M. King and H. Rob, and Sigesbeckia orientalis L. in order to describe the morpho-anatomy, ontogenetic steps, and identify features that may support the tribeal classification. Flowers and buds were fixed in glutaraldehyde, embedded in historesin, and sectioned with a rotary microtome. Sections were stained with Toluidine Blue. The inflorescence can be heterogamous or homogamous; the pappus is absent or persistent; the corolla is tubular or ligulate; anthers have an apical appendage which is obtuse or acute; and some anatomical features are the ovary usually trapezoidal-shaped; the pappus either vascularized or not; the corolla with possible secretory structures, only two species do not show twin hair on the outer ovary epidermis;and ovarian mesophyll usually composed of two or three regions. In general, the species analyzed show several similar features, such as the anther structure, pappus, and stigma. A distinct feature was observed among the species: the absence of pappus, and twin hairs in three species: E. alba (Heliantheae tribe), P. hysterophorus (Heliantheae tribe), and S. orientalis (Millerieae tribe), all belonging to ''Helliantheae Alliance'' clade.

Anatomical characteristics of Xeranthemum L. (Compositae) species: taxonomical insights and evolution of life form

“…Historically, Compositae represents difficulties for ontogenetic studies (Dadpour et al, 2012), and the available data regarding floral and inflorescence anatomy is still scarce. Batista & De Souza (2017) studied the floral ontogeny of ten Compositae species from Brazil and showed the usefulness of the flower characters in distinguishing species. Also, Franca et al, (2015) investigated embryology of two Ageratum L. species and confirmed heterogeneity of embryological processes within family.…”

Morphoanatomy of the inflorescence and flowers of Solidago chilensis (Asteraceae)

“…This would be achieved by interlocking the pointed papillary cells located on the margins of the lobes and their cuticular projections (Weberling 1989). The adhesion of petals by papilliform cells was also observed in species of several Asteraceae tribes (Batista and De Souza 2016).…”

“…In Solidago chilensis, the bristles do not have any vascular tissues, and according to Robinson (2009), they would be true bristles which are almost never vascularized. On the other hand, in Conyza bonariensis, another representative of Astereae, the pappus presents vascular tissues in its bristles (Batista and De Souza 2016). The pappus would protect the flowers during their development and also after anthesis (Robinson 2009).…”

“…The ovary in many species of Asteraceae presents a differentiated mesophyll in two or three histological zones (Batista and De Souza 2016). In the ovary of S. chilensis, the flowers have two parenchyma zones, as in most of the ovaries described for the family.…”

“…Bars: a, l, m: 40 µm; b, e, i, k: 100 µm; c, f, j: 20 µm; d: 5 µm; h, g: 10 µm ◂ Souza (2016) indicate that in general, floral anatomical characteristics in weeds of several Asteraceae tribes have little use in separating the species in a genus. On the contrary, the use of micromorphological characters, particularly floral, has been useful to differentiate species in the same genus and to delimit conflicting genera (Wetter 1983;Koch et al 2013;Batista and De Souza 2016;Via do Pico et al 2016). In addition, Ciccarelli et al (2007) studied biseriate glandular trichomes in ovaries of several Asteraceae tribes and concluded that although the characteristics are homogeneous in the same species, there are important interspecific variations, with diagnostic value.…”