Volume 8, Issue 1, 2014, Pages 87-126
Botanical Research Institute of Texas, 1700 University Drive, Fort Worth, TX 76107, United States
The genus Echinacea (Asteraceae) has importance economically, medicinally, and ornamentally. Endemic to North America, distribution is centered in the states of Arkansas, Kansas, Missouri, and Oklahoma. Native Americans of the central Great Plains used Echinacea as a highly prized medicinal plant panacea. This anatomical study is based on R.L. McGregor's taxonomic treatment of the genus Echinacea that included 11 taxa: E. angustifolia var. angustifolia, E. angustifolia var. strigosa, E. atrorubens, E. laevigata, E. pallida, E. paradoxa var. neglecta, E. paradoxa var. paradoxa, E. purpurea, E. sanguinea, E simulata, and E. tennesseensis. Anatomy of Echinacea tennesseensis was not included because live plants were not available. Plants were collected at the height of anthesis from the experimental gardens at the University of Kansas. Samples were prepared for microtome and free-hand sectioning and staining. Macromorphology and microanatomy are described here, and photomicrographs illustrate the adaxial epidermal cells of ray ligules. Tissue map line drawings illustrate the pattern and distribution of stem trichomes, epidermal cells, cortex, vascular bundles, and pith. Measurements were included for stem diameters, epidermis, collenchyma, parenchyma, xylem vessels, sclerenchyma fibers, xylem and phloem vascularization, protoxylem points, and location and number of secretory canals for each Echinacea taxon. Sclerenchyma fibers (sclerotic cells with a black phytomelanin substance) are located in the pith tissue of all the varieties of E. angustifolia. Tissue maps and photomicrographs illustrate petiole transections and the presence of brachysclerids (stone cells) in E. paradoxa var. neglecta which were found nowhere else in this study. Plants resulting from crossings and introgression between E. atrorubens and E. angustifolia had many intermediate characteristics and were called "race intermedia." This name has no nomenclatural standing but the plants were found to have unique ray ligule adaxial epidermal cells. These multicelluar structures consist of an enlarged basal cell with a neck and a catenuliform series of one, two, or three discrete pyramidal cells that have not been described for any member of the Asteraceae or other flowering plant. A key to Echinacea taxa that includes the distinctive micromorphology of ray ligule adaxial epidermal cells is presented. A discussion of the structure and function of ray ligule microanatomy is included as this relates to insect pollinators. Questions still remain concerning the constancy of anatomical characters over a broad range of habitats based on statistically sampled populations.
Dichotomous key; Echinacea (coneflower); Endangered species; Ligule adaxial epidermal cells; Macro-and microanatomy; Sclerotic and stone cells
ISSN: 19345259Source Type: Journal Original language: English
Document Type: Article
Publisher: Botanical Research Institute of Texas Inc.