BOTN 201 - Department of Biology - TAMU
Images of the Navasota Flora - 9 April 1995

This common mint Lamiaceae (Labiatae) of mesic woodlands in the Navasota Valley, Salvia lyrata, is part of a large genus (ca. 900 species) that has a worldwide distribution. The inflorescence shows sympetalous flowers arranged in whorls (verticillate) on a quadrangular rachis - all typical features of this large (7th largest in Texas with 31 genera and 115 species), important family. From the perspective of the pollen vector, the S. lyrata flower has a nice landing platform (bilabiate) and reproductive parts arranged to both deposit and collect pollen from the vector's back. However, Salvia is a bit different from most mints in that what appear to be four, dark blue anthers on this image represent fertile and sterile anther sacs from only two stamens. The connective is elongated in Salvia to form a 'teeter-totter' that presses the fertile anther sacs against the vector's back as it proceeds into the corolla tube. Vector-specific adaptations such as this are typical of the specialized Asteridae. While the androecium is a bit strange, the mature gynoecium of S. lyrata is typical of the family in that four 'nutlets' are produced from the bicarpellate ovary. A relative, Salvia azurea can be found in flower at Lick Creek Park a bit later in the growing season.

A conspicuous element of the largest flowering plant family, the Asteraceae (Compositae), 'thistles' of the genus Cirsium are distributed throughout the northern hemisphere (ca. 200 species). Aptly named, the local species now well into flower - C. horridulum - is a large, robust thistle. This is a discoid inflorescence in that in does not include 'ray' or 'ligulate' florets.

Many would call this (above) a 'buttercup'. However, a 'bee-eye' view of the local Oenothera speciosa (Onagraceae) reveals why this species is known locally as by the same 'common name'. As indicated by comparison of the two images, Ranunculus and Oenothera are quite different in terms of both floral structure and phylogenetic relationships. On side view, it is evident that Oenothera is epigynous with the hypanthium extending well beyond the ovary. A closer look with a portion of the hypanthium removed shows that the hypanthium tube encloses the style which emerges from the top of the inferior ovary and terminates in four branches which reflect a syncarpous gynoecium of four carpels. It is also evident that anther attachment is versatile and the pollen of this genus tends of hang together to form a 'stringy' array.


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Last updated by HDW on 10 April 1995