Molecular phylogeny of Gymnocalycium (Cactaceae): assessment of alternative infrageneric systems, a new subgenus, and trends in the evolution of the genus.
OBJECTIVE
The South American genus Gymnocalycium (Cactoideae-Trichocereae) demonstrates how the sole use of morphological data in Cactaceae results in conflicts in assessing phylogeny, constructing a taxonomic system, and analyzing trends in the evolution of the genus.


METHODS
Molecular phylogenetic analysis was performed using parsimony and Bayesian methods on a 6195-bp data matrix of plastid DNA sequences (atpI-atpH, petL-psbE, trnK-matK, trnT-trnL-trnF) of 78 samples, including 52 species and infraspecific taxa representing all the subgenera of Gymnocalycium. We assessed morphological character evolution using likelihood methods to optimize characters on a Bayesian tree and to reconstruct possible ancestral states.


RESULTS
The results of the phylogenetic study confirm the monophyly of the genus, while supporting overall the available infrageneric classification based on seed morphology. Analysis showed the subgenera Microsemineum and Macrosemineum to be polyphyletic and paraphyletic. Analysis of morphological characters showed a tendency toward reduction of stem size, reduction in quantity and hardiness of spines, increment of seed size, development of napiform roots, and change from juicy and colorful fruits to dry and green fruits.


CONCLUSIONS
Gymnocalycium saglionis is the only species of Microsemineum and a new name is required to identify the clade including the remaining species of Microsemineum; we propose the name Scabrosemineum in agreement with seed morphology. Identifying morphological trends and environmental features allows for a better understanding of the events that might have influenced the diversification of the genus.
Laboratorio de Biología Molecular, Instituto Multidisciplinario de Biología Vegetal (IMBIV), Universidad Nacional de Córdoba, Av. Velez Sarsfield 1609, X5016GCA, Córdoba, Argentina.
Pablo H
PH
Demaio
Michael H J
MH
Barfuss
Roberto
R
Kiesling
Walter
W
Till
Jorge O
JO
Chiapella
D001499:Bayes Theorem; D005075:Biological Evolution; D029421:Cactaceae / Q000033:anatomy & histology / Q000145:classification* / Q000235:genetics*; D018742:DNA, Chloroplast / Q000032:analysis; D019143:Evolution, Molecular; D005638:Fruit / Q000033:anatomy & histology; D005843:Geography; D008969:Molecular Sequence Data; D010802:Phylogeny; D018517:Plant Roots / Q000033:anatomy & histology; D018547:Plant Stems / Q000033:anatomy & histology; D012639:Seeds / Q000033:anatomy & histology; D017422:Sequence Analysis, DNA; D013020:South America
D018742:DNA, Chloroplast