The Vascular Flora of Granite Outcrops in the Central Mineral Region of Texas

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Abstract
The vascular flora of granite outcrops in the Central Mineral Region of Texas includes 381 spp. in 255 genera and 88 families. Approximately 40% of the species belong to 5 families: Poaceae (56), Asteraceae (39), Cyperaceae (19), Fabaceae (18) and Polypodiaceae (15). Thirty-four families and 189 genera are represented by 1 spp. The 23 spp. characteristic of granite outcrops display 5 distribution patterns: endemic, near-endemic, eastern, western and widespread. A comparison of the granite outcrop floras of central Texas and the southeastern USA shows relatively few genera and species common to both regions; the life-form spectra are essentially identical. Drought-adapted therophytes and hemicryptophytes are dominant in both regions. Apparently, granite outcrops provide similar types of microenvironments despite major differences in the climate and surrounding vegetation of each region. The much higher proportion of endemics among the characteristic plants of granite outcrops in the Southeast (17) vs. Texas (4) reflects a greater degree of geographical isolation and sharper discontinuity with the surrounding vegetation.