Epidermal crystals in Acalypha (Euphorbiaceae, Acalyphoideae) as a new taxonomic trait of the genus
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ORIGINAL ARTICLE
Epidermal crystals in Acalypha (Euphorbiaceae, Acalyphoideae) as a new taxonomic trait of the genus José María Cardiel1,2 · Iris Montero‑Muñoz1 · Emma Ortúñez1,2 · Elena Dorda1 · Irene Sancho‑García1 Received: 14 February 2020 / Accepted: 31 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The occurrence of epidermal crystals in the species of the genus Acalypha (Euphorbiaceae, Acalyphoideae) is described and analyzed. The epidermal surface of 190 Acalypha specimens, belonging to 110 species and subspecies, was studied with a scanning electron microscope (SEM), and the elemental composition of the found crystals was examined using energydispersive X-ray spectroscopy (EDS). The results show that 96.4 % of the studied species have epidermal crystals, mainly located on the leaf surface, but also on the bracts and flowers. The crystals exhibit significant variation, and four types of crystals are recognized: prismatic, styloids, stellate, and druses, which are, respectively, designated with Ac, Bc, Cc and Dc letters. We have not found any reference to stellate crystals in the angiosperm morphological or anatomical literature, and druses are observed and described under SEM in Acalypha for the first time. The elemental composition of the crystals shows that all of them exhibit typical peaks of calcium. We discuss the possible taxonomic importance of crystals, due to the association that some of these types of crystals have with groups of closely morphologically related species. We have not found a relation between the presence or the type of crystals and the habitat or distribution of the species that present them. We do not know other genera of Euphorbiaceae where the presence of crystals is so widespread, so we propose that they should be considered as a distinctive feature of this genus. Keywords Acalypha · Acalyphoideae · Crystals · Euphorbiaceae · Malpighiales
Introduction In plants, crystals are products of metabolism and can occur in almost every part, including both vegetative and reproductive organs (Franceschi and Nakata 2005; Rudall 2007). Mineral crystals usually contain calcium, in the form of calcium oxalate, the most abundant biomineral in living organisms (Arnott 1982), but sometimes also from magnesium, sulfur, strontium, or barium (He et al. 2012a, b). Calcium oxalate crystals are found in more than 215 families of Handling Editor: Jürg Schönenberger. * José María Cardiel [email protected] 1
Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, Postal Code 28049 Madrid, Spain
Centro de Investigación en Biodiversidad y Cambio Global (CIBC‑UAM), Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, Postal Code 28049 Madrid, Spain
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flowering plant (Franceschi and Horner 1980; Lersten and Horner 2009). The shape and distribution of the crystals are highly variable and have taxonomic relevance (Prychid and Rudall 1999; Cervantes-Martinez et al. 2005; Horner et al.
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