Phytotaxa 358 (2): 189–197 http://www.mapress.com/j/pt/ Copyright © 2018 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Duilio Iamonico: 8 Jun. 2018; published: 4 Jul. 2018 https://doi.org/10.11646/phytotaxa.358.2.6 189 Diversification of inflorescence types in Portulaca (Portulacaceae) and its systematic implications GILBERTO OCAMPO 1* & LAURA MAIR-SÁNCHEZ 2 1 Departamento de Biología, Centro de Ciencias Básicas, Universidad Autónoma de Aguascalientes. Avenida Universidad 940, Ciudad Universitaria, C.P. 20930. Aguascalientes, Aguascalientes, Mexico; gilberto.ocampo@edu.uaa.mx ORCID 0000-0001-9325-922X 2 Bosques International School. Avenida Paseo de la Soledad 169, Fracc. Trojes de Oriente, 2ª sección, C.P. 20115. Aguascalientes, Aguascalientes, Mexico * Author for correspondence Abstract Portulaca is the only genus in Portulacaceae and includes ca. 100 species with worldwide distribution. Inflorescence types in Portulaca have been used as an important character in infrageneric classifications and it has been suggested that capitula and solitary flowers derive from a cyme. The present paper focuses on the study of the diversification patterns of the inflorescence within Portulacaceae based on a phylogenetic approach. A phylogenetic framework was used to estimate the ancestral inflorescence type under parsimony and maximum likelihood criteria. The results, although ambiguous, suggest that a cymose inflorescence may have been the ancestral type for Cactineae. Diversification patterns within Portulacaceae are not clear, but it is plausible that capitula and solitary flowers are derived from a cymose inflorescence. In addition, the first two types may have evolved independently at least twice in the group. These results show that the inflorescence type has limited systematic utility, contrary to the current accepted infrageneric classifications of Portulaca, and only characterizes a group of Australian species with cymose inflorescences. Keywords: Cactineae, inflorescence evolution, Portulacineae, systematics Introduction Portulaca Linnaeus (1753: 445) is the only member of the recently re-circumscribed Portulacaceae Juss. (see Nyffeler & Eggli 2010, Hernández-Ledesma et al. 2015). Although the number of species of the family is not well known, some authors estimate that Portulacaceae might include from 15 to ca. 100 species (Legrand 1958, Geesink 1969). The variation of some characters (e.g., seed morphology, capsule lid, and inflorescence architecture) have been used to circumscribe infrageneric taxa (e.g., Poelnitz 1932, Legrand 1958, 1962, Geesink 1969). Although the morphological variation may be high, some traits seem to be homoplastic and have a low systematic value (e.g., Ocampo 2015). Inflorescence types are one of the morphological characters that have been used to propose subgeneric classifications within Portulaca. Legrand (1958) recognized six subgenera; flowers were considered to be arranged as cymes and capitula, or solitary ones. Legrand’s proposal included a very elaborated system, but he mainly studied American species and recognized that his classification scheme may be challenged when Australian and African taxa were included for analysis. On the other hand, Geesink (1969) studied a larger number of Australian species, although the total number of specimens and taxa was much lower compared to Legrand’s (1958) work. Nevertheless, the herbarium material that Geesink studied allowed him to propose an infrageneric classification strongly based on inflorescence types. Geesink (l.c.) considered the cyme-like inflorescences of some Australian species (subgenus Portulacella (F. Muell.) Legrand 1953: 4) as an ancestral character, following Troll’s hypothesis (1964) that inflorescence branching patterns are similar to those found on the rest of the plant. He used the inflorescence types and leaf arrangement for his proposal to consider two subgenera and he concluded that the head-like inflorescences and solitary flowers found in his subgen. Portulaca are a derived feature. Moreover, he stated that the genus originated in Australia, and provided a hypothesis of inflorescence evolution by considering capitula and solitary flowers derived from branch reduction of a cyme-like flower arrangement.