Appendices & Glossary - Botanical Research Institute of Texas

FLORAS: EVOLUTIONARY TAXONOMY OR PHYLOGENETIC SYSTEMATICS?/APPENDIX SIX 1187
FIG. 177/DENDROGRAM SHOWING RELATIONSHIPS OF SOME VERTEBRATE GROUPS. NOTE THE PARAPHYLETIC NATURE OF THE “REPTILIA” (WHEN CONSIDERED TO
INCLUDE TURTLES, LIZARDS, SNAKES, AND CROCODILES, BUT NOT BIRDS). FIGURE PRODUCED BY BRIT/AUSTIN COLLEGE; REPRODUCTION OF THIS IMAGE DOES NOT
REQUIRE COPYRIGHT PERMISSION.
FIG. 178/PHENETIC DISTANCE DIAGRAM; HORIZONTAL DISTANCE BETWEEN SPECIES INDICATES PHENETIC DIFFERENCE. NOTE THAT SPECIES F, WHILE MOST CLOSELY
RELATED PHYLOGENETICALLY TO SPECIES E, IS QUITE DIFFERENT IN TERMS OF PHENETICS. FIGURE PRODUCED BY BRIT/AUSTIN COLLEGE; REPRODUCTION OF THIS
IMAGE DOES NOT REQUIRE COPYRIGHT PERMISSION.
(Capparaceae) gave rise to the mustards (Brassicaceae)—both families are still useful and meaningful
concepts that can help us understand evolution and organize our thinking. Cronquist (1987) stressed
the need for paraphyletic groups, indicating that both evolutionary relationships and the amount of
evolutionary divergence among taxa is important. He said that “the reasons for this belief are rooted in
the historical and continuing function of taxonomy as a general-purpose system of classification that
can be used by all who are concerned with similarities and differences among organisms”—in other
words, diverse users of botanical information. While we believe it is critically important for
paraphyletic groups to be clearly distinguished from monophyletic groups, the usefulness of
paraphyletic taxa (e.g., effective communication, recognition of divergence, morphological similarities,
etc.) seems to be an important consideration.