Phylogenetic discordance and integrative species delimitation in the Mammillaria haageana species complex (Cactaceae).

Species complexes consist of very close phylogenetic relatives, where morphological similarities make it difficult to distinguish between them using traditional taxonomic methods. Here, we focused on the long-standing challenge of species delimitation in the Mammillaria haageana complex, a group that presents great morphological diversity that makes its taxonomy a puzzle. Our work integrates genomic, morphological, and ecological data to establish the taxonomic limits in the M. haageana complex, and we also studied the evolutionary relationships with the remainder of the M. ser. Supertextae species. Our genetic analyses, as well as morphological and ecological evidence, led us to propose that the M. haageana complex is made up of six distinct entities (M. acultzingensis, M. conspicua, M. haageana, M. lanigera, M. meissneri, and M. san-angelensis), mainly as a result of ecological speciation. A recent taxonomic proposal considered these taxa as a single species; therefore, we propose their recognition at the species level. Our results also show a high level of incomplete lineage sorting rather than reticulation, which is especially likely in recently diverged species such as those comprising M. ser. Supertextae. The species hypotheses proposed here may be useful in future extinction risk assessments and conservation strategies.

Phylogenetic and morphological analyses of Pilosocereus leucocephalus group s.s. (Cactaceae) reveal new taxonomical implications.

Pilosocereus is one of the Cactaceae family's most relevant genera in terms of the number of species and its wide geographical range in the Americas. Within Pilosocereus, five informal taxonomic groups have been recognized, one of which is P. leucocephalus group s.s., whose phylogenetic relationships remain unresolved. Therefore, our objectives are to recognize the circumscriptions of the species in P. leucocephalus group s.s. and to corroborate the monophyly and phylogenetic relationships of this group through a set of morphological and molecular characters. This study is based on representative sampling along the broad distribution of this group in Mexico and Central America using multivariate and phylogenetic analyses. The morphological characters identified to contribute to species recognition and group formation are branch diameter, areole length, the areole length-width ratio, the distance between areoles, the length of the longest radial spine, and branch and spines colors. The chloroplast markers rpl16, trnL-trnF, and petL-psbE and the nuclear marker AT1G18270 support the monophyly of the P. leucocephalus group s.s., and two probable synapomorphies are suggested, including one transversion in rpl16 and another in petL-psbE. Together, our results demonstrate that sampled species of P. leucocephalus group s.s. encompass six species distributed in Mexico and Central America: P. alensis and P. purpusii in the western region, P. chrysacanthus and P. collinsii in the central region, and P. gaumeri and P. leucocephalus in the eastern region. A taxonomic key to recognized species is provided.

Evolution of flower allometry and pigmentation in Mammillaria haageana (Cactaceae).

BACKGROUND: A puzzle in evolution is the understanding of how the environment might drive subtle phenotypic variation, and whether this variation is adaptive. Under the neutral evolutionary theory, subtle phenotypes are almost neutral with little adaptive value. To test this idea, we studied the infraspecific variation in flower shape and color in Mammillaria haageana, a species with a wide geographical distribution and phenotypic variation, which populations are often recognized as infraspecific taxa. RESULTS: We collected samples from wild populations, kept them in the greenhouse for at least one reproductive year, and collected newly formed flowers. Our first objective was to characterize tepal natural variation in M. haageana through geometric morphometric and multivariate pigmentation analyses. We used landmark-based morphometrics to quantify the trends of shape variation and tepal color-patterns in 20 M. haageana accessions, belonging to five subspecies, plus 8 M. albilanata accessions for comparison as the sister species. We obtained eight geometric morphometric traits for tepal shape and color-patterns. We found broad variation in these traits between accessions belonging to the same subspecies, without taxonomic congruence with those infraspecific units. Also the phenetic cluster analysis showed different grouping patterns among accessions. When we correlated these phenotypes to the environment, we also found that solar radiation might explain the variation in tepal shape and color, suggesting that subtle variation in flower phenotypes might be adaptive. Finally we present anatomical sections in M. haageana subsp. san-angelensis to propose some of the underlying tepal structural features that may give rise to tepal variation. CONCLUSIONS: Our geometric morphometric approach of flower shape and color allowed us to identify the main trends of variation in each accession and putative subspecies, but also allowed us to correlate these variation to the environment, and propose anatomical mechanisms underlying this diversity of flower phenotypes.

Growth Patterns in Seedling Roots of the Pincushion Cactus Mammillaria Reveal Trends of Intra- and Inter-Specific Variation.

Genetic mechanisms controlling root development are well-understood in plant model species, and emerging frontier research is currently dissecting how some of these mechanisms control root development in cacti. Here we show the patterns of root architecture development in a gradient of divergent lineages, from populations to species in Mammillaria. First, we show the patterns of variation in natural variants of the species Mammillaria haageana. Then we compare this variation to closely related species within the Series Supertexta in Mammillaria (diverging for the last 2.1 million years) in which M. haageana is inserted. Finally, we compared these patterns of variation to what is found in a set of Mammillaria species belonging to different Series (diverging for the last 8 million years). When plants were grown in controlled environments, we found that the variation in root architecture observed at the intra-specific level, partially recapitulates the variation observed at the inter-specific level. These phenotypic outcomes at different evolutionary time-scales can be interpreted as macroevolution being the cumulative outcome of microevolutionary phenotypic divergence, such as the one observed in Mammillaria accessions and species.

Evaluating the monophyly of Mammillaria series Supertextae (Cactaceae).

Mammillaria (Cactaceae) taxonomy has been historically problematic due to the morphological variability and sympatry of the species. This has led to several proposals for infrageneric classification, including subgeneric, section and series categories. Mammillaria ser. Supertextae is one of 15 series and is made up of a variable set of species that are mainly distributed in southern Mexico and Central America. However, the phylogenetic relationships within M. ser. Supertextae and its relationship to other Mammillaria taxa are far from fully understood. Here we attempt to elucidate these relationships using complete terminal sampling and newly obtained chloroplast marker sequences and comparing them to Mammillaria species sequences from GenBank. Our phylogenetic analyses showed that M. ser. Supertextae comprises a well-supported monophyletic group that diverged approximately 2.1 Mya and has M. ser. Polyacanthae as its sister group; however, relationships within M. ser. Supertextae remain unresolved. The topology obtained within M. ser. Supertextae must also be interpreted under the distribution shared by these taxa, but it is difficult to differentiate ancestral polymorphisms from possible introgression, given the short time elapsed and the markers used. Our results show that the infrageneric units of M. haageana and M. albilanata can be considered independent evolutionary units. We also suggest that the relationship between M. haageana and M. albilanata is convoluted because their distribution overlaps (mainly towards southern Mexico), with genetic differences that possibly indicate they represent more than two taxonomic entities. One possible explanation is that there could still be gene flow between these taxa, and we might be witnessing an ongoing speciation process.