Philip D. Cantino

Evidence for a polyphyletic origin of the Labiatae

A preliminary cladistic analysis suggests that the Labiatae are polyphyletic as presently circumscribed. The gynobasic-styled Labiatae emerge as a clade, nested within a larger group characterized by suprareticulate pollen and a fruit composed of nutlets. The latter includes the bulk of the Labiatae plus the verbenaceous genera Garrettia and Holmskioldia; its closest relatives are in tribe Viticeae (Verbenaceae). In contrast, Teucrium and five other genera of Ajugeae (Labiatae) belong to a large clade characterized by pollen with branched to granular columellae, most members of which are currently assigned to tribes Clerodendrea and Caryopterideae (Verbenaceae) (...)

Subfamilial Classification of Labiatae

A subfamilial level classification of Labiatae, originally proposed by G. Erdtman on the basis of pollen features, has received substantial corroboration in the European literature but remains little known in North America. In subfam. Lamioideae, pollen is usually tricolpate and shed in a two-celled stage; in subfam. Nepetoideae (Dumortier) Luerssen, it is usually hexacolpate and shed in a three-celled stage. The number of pollen cells and colpi are reported here for 108 genera of Labiatae, including 93 for which one or both had not previously been reported. The established relationship between number of colpi and pollen cells is consistent in 95% of the labiate genera for which data are available. In the remaining genera, one pollen character is constant while the other varies; in no genus is the pollen consistently tricolpate and three-celled when shed or consistently hexacolpate and two-celled. Other characters whose variation patterns closely parallel the pollen characters include occurrence of endosperm, embryo shape, cotyledon shape, volatile terpenoid content, occurrence of rosmarinic acid, occurrence of iridoid glycosides, degree of un- saturation of fatty acids in the seed oils, and myxospermy. Erdtmans subfamilies appear to be the primary phenetic groupings of the Labiatae, but only subfam. Nepetoideae can be shown to be monophyletic on the basis of synapomorphies. Briquets (1895-1897) widely used classification is highly incongruent with Erdtmans, and it is recommended that the former be abandoned. A tabulation is provided of the component genera of each of Erdtmans subfamilies, along with the character state data upon which subfamilial assignments were based.

Vegetation patterns and structure of an old-growth forest in southeastern Ohio

MCCARTHY, B. C. (Dept. of Biological Sciences, Rutgers University, P.O. Box 1059, Piscataway, NJ 08855), C. A. HAMMER, G. L. KAUFFMAN AND P. D. CANTINO (Dept. of Botany, Ohio University, Athens, OH 45701). Vegetation patterns and structure of an old-growth forest in southeastern Ohio. Bull. Torrey Bot. Club 114:33-45. 1987.-A large, minimally disturbed, and floristically diverse old-growth forest (Hawk Woods) on the Allegheny Plateau in southeastern Ohio was studied to compare woody vegetation structure, composition, and soils both within and among communities. Five vegetation types were initially identified based on visual estimates of dominance and indicator species: mixed mesophytic, mixed oak-tulip poplar, white oak, oak-hickory, and oak-heath. Principal components ordination did not reveal distinct groupings of stands within and among vegetation types. Further quantitative analysis suggested that fewer ecological groupings were sufficient to describe vegetation types. Cluster analysis supported three ecological groupings apparently related to a topographic-moisture continuum. Multivariate analysis of variance of soil variables indicated significant differences among stands. Linear correlation of soil variables with principal components suggested the presence of a soil nutrient gradient associated with the topographic-moisture gradient. Edaphic parameters were not useful for discriminating community types but did however covary with the vegetation continuum. Size-class analysis of vegetation types indicated similarities and differences both among communities within Hawk Woods and among other forests in the Plateau region. Diameter distribution curves for vegetation types were observed to fit the negative power function more closely than the negative exponential function. Size-class distributions of individual species varied, apparently as a function of broad-scale ecological characteristics (e.g., shade tolerance). Quercus spp. exhibited marked underrepresentation in the smaller size-classes, suggesting an inability to self-perpetuate.

A review of criticisms of phylogenetic nomenclature: is taxonomic freedom the fundamental issue?

The proposal to implement a phylogenetic nomenclatural system (governed by the PhyloCode), in which taxon names are defined by explicit reference to common descent, has met with strong criticism from some proponents of phylogenetic taxonomy (taxonomy based on the principle of common descent in which only clades and species are recognized). We examine these criticisms and find that some of the perceived problems with phylogenetic nomenclature are based on misconceptions, some are equally true of the current rank‐based nomenclatural system, and some will be eliminated by implementation of the PhyloCode. Most of the criticisms are related to an overriding concern that, because the meanings of names are associated with phylogenetic pattern which is subject to change, the adoption of phylogenetic nomenclature will lead to increased instability in the content of taxa. This concern is associated with the fact that, despite the widespread adoption of the view that taxa are historical entities that are conceptualized based on ancestry, many taxonomists also conceptualize taxa based on their content. As a result, critics of phylogenetic nomenclature have argued that taxonomists should be free to emend the content of taxa without constraints imposed by nomenclatural decisions. However, in phylogenetic nomenclature the contents of taxa are determined, not by the taxonomist, but by the combination of the phylogenetic definition of the name and a phylogenetic hypothesis. Because the contents of taxa, once their names are defined, can no longer be freely modified by taxonomists, phylogenetic nomenclature is perceived as limiting taxonomic freedom. We argue that the form of taxonomic freedom inherent to phylogenetic nomenclature is appropriate to phylogenetic taxonomy, in which taxa are considered historical entities that are discovered through phylogenetic analysis and are not human constructs.

Paraphyly, ancestors, and the goals of taxonomy: A botanical defense of cladism

Cronquist (1987) criticizes cladism for its rejection of paraphyletic groups, which he would retain if he feels they are “conceptually useful.” We argue that paraphyletic higher taxa are artificial classes created by taxonomists who wish to emphasize particular characters or phenetic “gaps,” and that formal recognition of such taxa conveys a misleading picture of common ancestry and character evolution. In our view, classifications should accurately reflect the nested hierarchy of monophyletic groups that is the natural outcome of the evolutionary process. Such systems facilitate the study of evolution and provide an efficient summary of character distributions. Paraphyletic groups, such as “prokaryotes,” “green algae,” “bryophytes,” and “gymnosperms,” should be abandoned, as continued recognition of such groups will only serve to retard progress in understanding evolution. Contrary to Cronquist’s (1987) assertions, cladistic theory is not at odds with standard views on speciation and the existence of ancestors. Groups of interbreeding organisms can continue to exist after giving rise to descendant species, and there are several ways in which such groups, whether extant or extinct, can be incorporated into cladistic classification. In contrast, paraphyletic higher taxa are neither cohesive (integrated by gene flow) nor whole, do not serve as ancestors, and are unacceptable in the phylogenetic system. Fossils may be of great value in assessing phylogenetic relationships and are readily accommodated in cladistic classification. Cladistic studies are helping to answer major questions about plant evolution, and we anticipate increased efforts to develop a truly phylogenetic system.RésuméCronquist (1987) critique le cladisme pour son rejet des groupes paraphylétiques, qu’il voudrait conserver quand ceux-ci sont “conceptuellement utiles.” Nous avançons l’argument que les taxons supérieurs paraphylétiques sont des groupes artificiels, définis par des taxonomistes qui désirent souligner certains caractères ou certaines “lacunes” phénétiques, et que la reconnaissance formelle de tels groupes donne une fausse impression de descendance commune et sur l’évolution de caractères. À notre avis, une classification doit refléter fidèlement la hiérarchie des groupes monophylétiques emboités, le résultat naturel du processus de l’évolution. Ces classifications facilitent l’étude de l’évolution et fournissent d’efficaces sommaires de la distribution phylétiques des caractères. La reconnaissance des groupes paraphylétiques, tels les “Prokaryotes,” les “Algues vertes,” les “Bryophytes,” et les “Gymnospermes,” devrait etre abandonnée, car elle ne peut que retarder notre compréhension de l’évolution. Contrairement à ce que Cronquist suggère, l’analyse cladistique n’est pas en désaccord avec les vues classiques sur la spéciation et l’existence d’ancêtres. Les groupes d’individus unifiés par le flux génétique peuvent continuer à exister après avoir donné souche à une nouvelle espèce, et il y a plusieurs moyens d’incorpores de tels groupes, qu’ils soient actuels ou disparus, dans une classification cladistique. Par contre, les taxons supérieurs paraphylétiques ne sont ni cohésifs (unifiés par le flux génétique) ou entiers, ne peuvent pas servir d’ancêtres, et sont inacceptables dans un systeme phylogénétique. Les fossiles peuvent être très utiles pour évaluer les rapports phylogénétique, et sont aisément incorporés dans une classification cladistique. Les analyses cladistiques contribuent à la solution de questions majeures de l’évolution des plantes, et nous prévoyons des efforts renouvelés pour le développement d’un systême réellement phylogénétique.

The logic and limitations of the outgroup substitution approach to cladistic analysis

The outgroup substitution approach can be used when a well-corroborated hypoth- esis of the more inclusive cladistic relationships of a study group is unavailable. It is particularly appropriate when the set of outgroups, each of which could plausibly be the sister group, includes some that may be only distantly related to others. All plausible sister groups are used as outgroups, alone and in various arrangements, to assess character polarities. In each case an ingroup cladogram is constructed and these are searched for areas of congruence. Through this approach, robust phylogenetic hypotheses can be generated in spite of uncertain outgroup relationships. Caution must be exercised because polarity assessment is sensitive to the exact arrangement of outgroups. Even if completely congruent cladograms are obtained, it may not be possible to specify character support for particular clades. The approach may be most useful when ones primary objective is to establish an outgroup hypothesis for a subsequent cladistic analysis at a lower taxonomic level.

Affinities of the Lamiales: A Cladistic Analysis

The Boraginaceae and Scrophulariales have each been proposed as the closest extant relative of the Lamiales (i.e., Labiatae plus Verbenaceae). Char- acters supporting the two hypotheses are evaluated in light of cladistic principles. Character polarity is determined primarily through outgroup comparison. Because of uncertainty about the identity of the outgroup, separate analyses are conducted in relation to five possible outgroups. No matter which is used, there are more synapomorphies uniting the Lamiales with the Scrophulariales than with the Bora- ginaceae. This analysis departs from a strict Hennigian approach in permitting some variation within both the outgroup and the ingroup in characters used as synapo- morphies. The magnitude of variation in many higher taxa of plants renders im- practical a strict approach requiring consistent character differences. The use of apomorphic tendencies and judicious application of the commonality principle are advocated as means to tentative groupings in such cases. A survey of published phylogenies reveals two opposing viewpoints concerning the closest extant relatives of the Lamiales (i.e., Labiatae plus Verbenaceae; see below). Some authors (Hallier 1912; Dahlgren 1977, 1980; Wagenitz 1977) have asserted that the Scrophulariales is the extant group most closely related to these families, while others have claimed this position for the Boraginaceae s.l. (Wernham 1911; Thorne 1976, 1981; Takhtajan 1980; Cronquist 1981). Proponents of each view stress those characteristics that appear to unite the Labiatae and Verbenaceae with the putatively related group, sometimes attributing to convergence those traits that support the opposing view. It is my intent in this paper to evaluate the two hypotheses in light of cladistic principles. The crux of Hennigian cladistic analysis (Hennig 1966; Bremer and

Species Names in the PhyloCode: The Approach Adopted by the International Society for Phylogenetic Nomenclature

Edwards, S. V., L. Liu, and D. K. Pearl. 2007. High resolution species trees without concatenation. Proc. Natl. Acad. Sci. USA 104:5936– 5941. Hennig, W. 1950. Grundzuge Einer Theorie der Phylogenetischen Systematik. Deutscher Zentralverlag, Berlin. [Published in English translation in 1966: Phylogenetic systematics, University of Illinois Press, Urbana, Illinois.] Hudson, R. R. 1983. Testing the constant-rate neutral allele model with protein sequence data. Evolution 37:203–217. Liu, L., and D. K. Pearl. 2007. Species trees from gene trees: Reconstructing Bayesian posterior distributions of a species phylogeny using estimated gene tree distributions. Syst. Biol. 56:504–514. Maddison, W. P. 1997. Gene trees in species trees. Syst. Biol. 46:523– 536. Maddison, W. P., and L. L. Knowles. 2006. Inferring phylogeny despite incomplete lineage sorting. Syst. Biol. 55:21–30. Nei, M. 1987. Molecular evolutionary genetics. Columbia University Press, New York. Neigel, J. E. and J. C. Avise. 1986. Phylogenetic relationships of mitochondrial DNA under various demographic models of speciation. Pages 515–534 in Evolutionary processes and theory (S. Karlin and E. Nevo, eds.). Academic Press, Orlando, Florida. Nichols, R. 2001. Gene trees and species trees are not the same. Trends Ecol. Evol. 16:358–364.

Systematic implications of pollen morphology in Caryopteris (Labiatae)

Caryopteris, an Asian genus of 16 species, has greater pollen diversity than has been reported in any other genus of Labiatae. The pollen morphology of 15 species is documented here. Three pollen types are distinguished on the basis of exine structure and sculpturing: spinulose to spinose with slender, finely divided columellae (alternatively interpretable as an expanded tectum); verrucate with a well defined tectum and thick, sparsely branched columellae; and suprareticulate to microreticulate with moderately thick, sparsely branched columellae. Thirteen species are tri- colpate, Caryopteris divaricata is triporate, and C. nepalensis is 6-pantocolpate. Pollen morphology and correlated variation in floral and fruit morphology suggest that Caryopteris comprises three primary phenetic groups. However, two recent cladistic analyses (one based in part on the pollen features documented here) indicate that the genus is para- or polyphyletic and that only one of the three phenetic subgroups is clearly monophyletic. Recircumscription of the genus is recommended, but this should await completion of current studies that will facilitate its subdivision into monophyletic taxa.

Chromosome Studies in Subtribe Melittidinae (Labiatae) and Systematic Implications

Chromosome numbers are documented for the first time for Brazoria, Macbridea, and Synandra. The latter two have 2n = 18. Brazoria comprises two cytologically distinct subgroups: 1) B. scutellarioides, with 2n = 20 plus one to four small bodies interpreted as supernumerary chro- mosomes, and 2) B. arenaria, B. pulcherrima, and B. truncata, with 2n = 28 and lacking supernumer- ary chromosomes. Chromosomal data corroborate morphologically circumscribed subgroups within Brazoria and provide weak support for a relationship between Macbridea and Synandra.