Aliso 22, pp. 28–51 2006, Rancho Santa Ana Botanic Garden PHYLOGENETIC RELATIONSHIPS OF MONOCOTS BASED ON THE HIGHLY INFORMATIVE PLASTID GENE ndhF: EVIDENCE FOR WIDESPREAD CONCERTED CONVERGENCE

We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 monocot families and all 12 orders. The resulting tree is highly resolved and places commelinids sister to Asparagales, with both sister to Liliales–Pandanales in the strict consensus; Pandanales are sister to Dioscoreales in the bootstrap majority-rule tree, just above Petrosaviales. Acorales are sister to all other monocots, with Alismatales sister to all but Acorales. Relationships among the four major clades of commelinids remain unresolved. Relationships within orders are consistent with those based on rbcL, alone or in combination with atpB and 18S nrDNA, and generally better supported: ndhF contributes more than twice as many informative characters as rbcL, and nearly as many as rbcL, atpB, and 18S nrDNA combined. Based on functional arguments, we hypothesized that net venation and fleshy fruits should both evolve—and thus undergo concerted convergence—in shaded habitats, and revert to parallel venation and dry, passively dispersed fruits in open, sunny habitats. Our data show that net venation arose at least 26 times and disappeared 9 times, whereas fleshy fruits arose 22 times and disappeared 11 times. Both traits arose together at least 15 times and disappeared together 5 times. They thus show a highly significant pattern of concerted convergence (P 10 9) and are each even more strongly associated with shaded habitats (P 10 10 to 10 23); net venation is also associated, as predicted, with broad-leaved aquatic plants. Exceptions to this pattern illustrate the importance of other selective constraints and phylogenetic inertia.