BOTN 201 - Department of Biology Herbarium - TAMU
Images of the Navasota Flora - 2 July 1995
Local species of the genus Ruellia (Acanthaceae Asteridae Scrophulariales) tend to flower in mid-summer. In reproductive parts; four, epipetalous (adnate to the corolla) stamens and a bifid stigma with one of the stigma lobes much smaller than the other. As indicated, the pollen grains are quite large, probably because the microgametophytes, placed on the asymmetrical stigma, must grow through a ovary. Once this is accomplished, the ovary explosively dehiscent capsule. Explosive dehiscence, a distinctive feature of the Acanthaceae, is produced by two structural adaptations; differential pericarp maturation to produce tension along the suture and specialized, hook-like '
Prairie Parsley (Polytaenia nuttallii) represents another family - the Apiaceae (Umbelliferae) - that is marked by specialized adaptations of the mature gynoecium. Large local plants, in full flower a few weeks ago, are now setting fruit. Fruit of the Apiaceae are schizocarpic, separating at maturity into two carpellary units (mericarps), each containing a single seed. Pericarp modifications of each mericarp are often targeted for dispersal. Animal-adapted taxa, such as Sanicula often carry hook-like structures while those adapted for wind dispersal, like Polytaenia nuttallii, have developed wing-like extensions. Once the mericarps are fully mature they separate and hang suspended on delicate carpophores poised for travel away from the parent plant on the next gust of wind.
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Last updated by HDW on 3 July 1995