Morphological Diversity and Taxonomic Importance of Fruits and Seeds of the Genus Spigelia (Loganiaceae) in Mexico

Abstract

Abstract— The genus Spigelia (Loganiaceae) is a Neotropical genus that includes more than 80 species distributed from the United States to Argentina. Systematic studies of the group have rarely considered the carpological characters, so their taxonomic importance has not been analyzed in detail. The aim of this study is to analyze the morphological characteristics of these organs to provide more information for a better species separation and for a more robust infra-generic classification. We provide a detailed description of Spigelia fruits and seeds of the Mexican species since the country represents one of its main centers of diversification. Fruits and seed samples from 54 individuals across 14 species were measured and photographed to describe each one, maintaining as much detail as possible. With the morphological matrix a DFA, PCA, and a dendrogram using the NJ method was performed. The fruits and seeds of the Mexican Spigelia species proved to be taxonomically useful, allowing the differentiation of four main clusters of species separated by the size of the analyzed structures in the three analyses (DFA, PCA, NJ). The results show the variation in size and shape of the structures analyzed, which shows the taxonomic importance of fruits and seeds of the genus Spigelia. Our work represents an advance in the detailed knowledge of structures, which are rarely considered in the descriptions, and which allows us to have a separation of species. A taxonomic treatment and photographs of the fruits and seeds are also included.

Sinopsis del género Spigelia (Loganiaceae) en Norteamérica, Centroamérica y el Caribe

“…These characteristics, such as the presence of stipules or the phyllotaxis below the inflorescences, allow, in the absence of flowers, to approach to the identification of the species, which can be subsequently corroborated with the help of the diagnoses. Likewise, it has been observed that carpological characters present an important variation that allows the delimitation of species for their identification, even if the plant no longer has flowers or fruits (Islas-Hernández et al, 2022).…”

“…The detailed knowledge of the morphological structures that help to identify the species (e.g., type of style, pollen, carpoatlas or shape of the seeds), can be integrated as morphological markers, which together with the molecular markers will allow in the future to generate combined phylogenetic analyzes (Peterson and Seberg, 1998). In this sense, the use of carpological characters for the separation of groups of species has been studied within the genus (Islas-Hernández et al, 2022), and this information will allow, together with the floral information, the proposal of new sections that have phylogenetic congruence (Gould, 1997) and that are complemented with information derived from the species of the SA region.…”

“…In APG IV (APG, 2016), the classification followed in the present work, the genus remains within the Loganiaceae family, in its monogeneric tribe Spigelieae with about 90 species reported for the American continent (Stevens, 2001). However, the relationships within the group have not yet been resolved, and the proposed sections have been rejected because they are based on few morphological characters (Islas-Hernández et al, 2022), some of which are associated with evolution by convergence (Gould, 1997).…”

“…The testa has a sulcate, reticulated, rough, scaly or foveolate ornamentation, verrucate or smooth in the depressions. The seeds mainly have a pyramidal shape, where it is easy to distinguish a highly ornamented dorsal and a ventral face where the hilum is in a depression; in some cases, they become compressed (Fernández-Casas, 2003a;Islas-Hernández et al, 2022). = Pseudospigelia W. Klett, Bot.…”

“…The use and increase of characters, such as pollen and seeds, and the use of other evaluation tools will allow proposing more natural infrageneric classifications. Within the genus Spigelia, the use of carpological morphology has been of great help in the separation of groups that present an important correlation with floral and pollen characters, as well as with their distribution (Islas-Hernández et al, 2022). Macedo and Buril (2021), isolectotypes: GH-72226!, NY-277648!…”