Lecture 5

Asteraceae

Asteraceae:

One of the two largest families of flowering plants (the other family is the orchid family

In the Louisiana flora the family is the largest in terms of number of species.

Recognition factors include:

Inflorescence a head or capitulum surrounded by an involucre of bracts called phyllaries. The latter are attached to the outer or lower part of the compound receptacle.

Two types of flowers potentially found in the capitulum are the disk and ray flowers are attached to the inner or upper part of the compound receptacle.

In heads having both disk and ray flowers, the disk are located in the center with the rays around the periphery or margin just inside the inner row of phyllaries. Such heads having both disk and ray flowers are called radiate; examples include Aster, Helianthus, and Helenium. Discoid heads have only disk flowers; Eupatorium and Vernonia are examples. Ligulate heads have only ray flowers; an example is Lactuca. Receptacular bracts (chaff) are associated with each disk flower in certain species of Asteraceae; Helianthus is an example.

Disk and ray flowers are epigynous. Pappus occupies the position of sepals; the corolla typically consists of five fused petals. In the disk the corolla has radial symmetry while in the ray the symmetry is bilateral. The anthers are fused forming a collar around the style and the filaments are epipetalous. The style branches are two per flower. Ray flowers are typically sterile, showy, and function in attracting animal pollinators. The disk flowers are less conspicuous and function in pollen and seed production.

There are several wetland species in our regional flora:

3 species that are shrubs:

1 species that is a vine:

Other wetland commonly encountered taxa:

Aster subulatus, Aster tenuifolius, Aster spinulosus (Chloracantha spinosa, Ambrosia trifida, Ambrosia artemisiifolia, [Ambrosia psilostachya], Bidens laevis, Bidens spp., Boltonia asteroides, Carphephorus pseudoliatris, Bigelowia nudata, Eclipta prostrata (Eclipta alba), Eupatorium spp., Solidago semprevirens, Helenium spp., Helianthus heterophyllus, Helianthus simulans, Iva annua, Liatris spp., Pluchea spp., Solidago semprevirens, Spilanthes americana (Acmella oppositifolia), Verbesina spp., Vernonia gigantea.