A Morphometric Analysis of the Santolina chamaecyparissus Complex (Asteraceae)

Abstract

The genus Santolina (Asteraceae, Anthemideae) includes 26 species of aromatic evergreen shrubs endemic to the western Mediterranean Basin. Santolina is widely used as ornamental plant, in xerigardening, and in ethnobotany. The Santolina chamaecyparissus complex, including about half of the known species diversity, has been properly investigated on systematic and taxonomic grounds only recently, and a complete morphometric study is still missing. Here we provide a morphometric characterization and comparison of all the 14 species of this complex, using both univariate and multivariate analyses. Our results suggest that species of this complex can be distinguished using combinations of quantitative and qualitative character-states, mostly related to the leaf morphology. The analysis of S. villosa, a tetraploid/hexaploid Spanish endemic, showed that the two cytotypes cannot be safely identified based on morphology. Coupling this evidence with available phylogenetic information, we conclude that there is no reason to split the two cytotypes of S. villosa in two distinct taxa. An identification key for all the species of the complex is presented.

An integrative taxonomic study of Santolina (Asteraceae) from southern France and north‐eastern Spain reveals new endemic taxa

“…The populations analyzed in this study (Table 1) are the same as those sampled by Giacò et al (2022) in southern France and north‐eastern Spain: the populations from type localities of Santolina benthamiana , Santolina decumbens , and Santolina ericoides (Fig. 1); a population collected at the foothills of the French Pyrenees, from an area where populations morphologically intermediate between S. benthamiana and S. ericoides are reported (Giacò et al, 2021) (Ben‐rou in Table 1); a population of S. decumbens located at the northernmost portion of its species range (Dec‐sis in Table 1); an isolated population of S. decumbens located at the westernmost portion of its species range (Dec‐lfo in Table 1); and two populations of S. ericoides from north‐eastern Spain.…”

“…As outgroups, Achillea millefolium L. from NCBI and two populations of Santolina villosa Mill. (the same as those sampled in the karyo‐morphological study by Giacò et al, 2022) were used. For A. millefolium , we extracted the above‐mentioned markers from the plastid genome available on NCBI (accession no.…”

“…The Santolina chamaecyparissus L. species complex is an example of a group with an alpha‐taxonomic status, for which an integrated systematic approach is currently being carried out (Giacò et al, 2022; De Giorgi et al, 2022). Except for the cytotaxonomic studies conducted by Marchi & D′Amato (1973), Marchi et al (1979), and Valdés‐Bermejo & Antúnez (1981), the taxonomic circumscription of species within this complex is mostly based on qualitative morphological observations (Arrigoni, 1982; Tison & de Foucault, 2014; Carbajal et al, 2019).…”

“…Giacò et al (2021) also pointed out that four names, currently provisionally considered as synonyms of S. benthamiana , are based on type specimens that actually also show some morphological features that are otherwise typical of S. ericoides . A recent karyomorphological study (Giacò et al, 2022) demonstrated that all the Santolina populations native to southern France and north‐eastern Spain are diploid, with 2 n = 18 chromosomes. Therefore, the current taxonomic delimitation of Santolina species from southern France and north‐eastern Spain is based exclusively on qualitative morphological observations (Tison & de Foucault, 2014; Tison et al, 2014).…”

A guide to plant morphometrics using Gaussian Mixture Models

“…failing to reveal groups in the data) (Chang, 1983), 2) to compress information in fewer dimensions (Kuhn & Silge, 2022), or 3) to have another view of the multivariate data both in Q or R mode (Blackith & Reyment, 1971;Podani, 2007;Pagès, 2014). This behavior of PCA is more evident while attempts to perform genus-level exploration of the morphometric matrix using PCA or similar linear dimensionality reduction (DR) often led to an indistinguishable cloud of points since the overall variability is too spread among groups, forcing the user to use the sample centroids (Giacò et al, 2022) or to run a DR on portion of the dataset (Bateman & Rudall, 2023). This approach may lead to the loss of patterns that were actually present in the data while comparing fewer populations or species, leaving taxonomists with more uncertainties than answers (Rohlf & Bookstein, 1990).…”