Phenotypic variation in arid and semi-arid zones of southern South America: the case of Senna series Aphyllae (Fabaceae, Caesalpinioideae)

Abstract

Senna series Aphyllae includes xeromorphic shrubs and subshrubs that occur in three different biogeographic subregions in arid and semi-arid habitats of southern South America. The series provides a good opportunity to understand better the relationship among geographical, climatic, and morphological variation in different taxa. Moreover, in this group the specific and varietal delimitation is still problematic due to the high morphological variation within and among taxa. Statistical analyses of climatic and morphological data and geographical distribution were used to understand the patterns of morphological variation among 394 individuals and to clarify the taxonomic delimitation of entities that belong to series Aphyllae. Senna acanthoclada and S. nudicaulis were segregated from each other and from the remaining taxa; the three recognized varieties of the S. aphylla complex were delimited; S. spiniflora was well-delimited and S. crassiramea and S. rigidicaulis were overlapping; S. pachyrrhiza was not differentiated from S. aphylla. Ecological niche modelling showed several areas of contact and a large overlap of suitable conditions for several species. The results of this work revealed that most morphological variability is associated with different environmental conditions. This phenotypic plasticity may be caused by the presence of different environments with climatic factors in the South American Transition Zone, Chaco, and northern region of Central Patagonia province.

A New Insight Into the Classification of Senna Series Aphyllae (Leguminosae)

“…and S. pachyrrhiza could not be distinguished from S. aphylla var. divaricata (Robbiati et al, 2017a). Interestingly enough, we have observed in the field some characters used to differentiate Senna pachyrrhiza -such as pseudo-decumbent stems, terminal spinose branchlets and sand dwarf habit-in individuals of S. aphylla var.…”

“…Senna pachyrrhiza is morphologically similar to S. aphylla var. divaricata, both sharing flexuous branchlets and decumbent to pseudodecumbent stems and their preference for salty and sandy soils (Robbiati et al, 2017a). It has a peculiar geographical distribution, since it is an endemism of the "Campo del Arenal", an extensive plain of about 2000 km 2 , delimited by a group of mountains belonging to the "Sierras Pampeanas" system (Nores, 1986) in the Monte province.…”

“…Interestingly enough, we have observed in the field some characters used to differentiate Senna pachyrrhiza -such as pseudo-decumbent stems, terminal spinose branchlets and sand dwarf habit-in individuals of S. aphylla var. divaricata at high elevation in the steppe, in the Patagonian province; in addition, plant height in the series is correlated with elevation (Robbiati et al, 2017a). Furthermore, the overlapping distribution of all these taxa in the Monte province plus the ecological niche modeling, have shown several areas of contact and a large overlap in zones of suitable conditions (Robbiati et al, 2017a).…”

“…divaricata at high elevation in the steppe, in the Patagonian province; in addition, plant height in the series is correlated with elevation (Robbiati et al, 2017a). Furthermore, the overlapping distribution of all these taxa in the Monte province plus the ecological niche modeling, have shown several areas of contact and a large overlap in zones of suitable conditions (Robbiati et al, 2017a). Then, based on morphology, distribution and phylogenetic evidence, we propose to transfer from Senna aphylla the varieties divaricata and pendula to S. pachyrrhiza.…”

“…Based on phenetic and seed protein profiles we reinterpreted Aphyllae's taxonomy proposing seven species and three varieties (Robbiati et al, 2013(Robbiati et al, , 2014a(Robbiati et al, , 2014b. Afterwards, by means of statistical analyses of climatic and morphological data, and geographical distribution, we tried to understand the patterns of morphological variation among individuals to clarify the taxonomic delimitation of the entities involved in the series (Robbiati et al, 2017a). Furthermore, we investigated the evolutionary history of Aphyllae in a molecular phylogenetic framework (Robbiati et al, 2017b).…”