ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...
ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...
ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...
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204 INTRODUCTION/ORIGIN AND DIVERSITY <strong>OF</strong> <strong>EAST</strong> <strong>TEXAS</strong> <strong>FLORA</strong><br />
Spongberg 1983; Hamilton 1983; Hsü 1983; Wu 1983; Ying 1983; Cox & Moore 1993;<br />
Stuckey 1993; Xiang et al. 1998; Wen 1999, 2001; Xiang & Soltis 2001). Examples of East<br />
Texas genera found in all four of these areas include Cercis (Fig. 116), Aesculus, Erythronium,<br />
Juglans, Ostrya, Philadelphus, and Platanus (Wood 1970, 1972). Other East Texas genera (e.g.,<br />
Liquidambar) survive in only three of the four areas (Fig. 117) (Wood 1972). In addition, some<br />
groups which today are found in only one or two of the relict areas are known as fossils from<br />
other relict areas—examples include Nyssa (Fig. 117), Ailanthus, Dulichium, Ginkgo, Halesia,<br />
Metasequoia, and Taxodium, all of which had much broader Tertiary distributions than at<br />
present (Wood 1970; Manchester 1999).<br />
Because the Tertiary flora suffered in the center of North America, some groups remain<br />
today in separate eastern and western regions of the continent. Wood (1970) and Thorne<br />
(1993d) estimated that about 65% of the genera of southern Appalachian seed plants also occur<br />
in western North America and emphasized the strong floristic relationships between eastern and<br />
western North America. Numerous genera are found today only in these two separate areas—<br />
examples of East Texas genera with such a distribution include Ceanothus, Collinsia, Eriogonum,<br />
Oxypolis, Pycnanthemum, Schoenolirion, and Trichostema (Wood 1970). Even some species show<br />
this disjunct distribution on the two sides of the continent—e.g., three-way sedge, Dulichium<br />
arundinaceum (Fig. 118); brownish beak sedge, Rhynchospora capitellata (Fig. 119); globe beakrush,<br />
Rhynchospora globularis; and flux-weed, Isanthus brachiatus (Wood 1972). Likewise, Wen<br />
(1999) indicated that “there is a closer biogeographic relationship between eastern North<br />
America and western North America than between eastern North America and eastern Asia,”<br />
often with the phylogenetically most closely related species being in the two regions of North<br />
America. According to Xiang et al. (1998), about 30 genera have closely related species in both<br />
FIG. 118/GENERALIZED DISTRIBUTION MAP <strong>OF</strong> DULICHIUM ARUNDINACEUM (CYPERACEAE) (THREE-WAY SEDGE), AN EXAMPLE <strong>OF</strong> A SPECIES DIS-<br />
JUNCT BETWEEN <strong>EAST</strong>ERN AND WESTERN NORTH AMERICA.ALSO NOTE THE FOSSIL OCCURRENCE (TERTIARY) IN EUROPE (FROM WOOD 1972,<br />
WITH PERMISSION <strong>OF</strong> THE MISSOURI BOTANICAL GARDEN).<br />
FIG. 119/GENERALIZED DISTRIBUTION MAP <strong>OF</strong> RHYNCHOSPORA CAPITELLATA (CYPERACEAE) (BROWNISH BEAK SEDGE), AN EXAMPLE <strong>OF</strong> ASPECIES<br />
DISJUNCT BETWEEN <strong>EAST</strong>ERN AND WESTERN NORTH AMERICA (FROM WOOD 1972, WITH PERMISSION <strong>OF</strong> THE MISSOURI BOTANICAL GARDEN).