Laticifers are present in Acalyphoideae after all: new insights from leaf anatomy with implications for the systematics and evolution of Euphorbiaceae

Euphorbiaceae is among the main angiosperm families with a high number of laticiferous species. Although many of its species remain to be studied in terms of their anatomy, chemistry, and uses, there are some of recognized economic importance due to useful secondary compounds present in the latex. Acalyphoideae, one of the three major subfamilies, has traditionally been distinguished from the rest of Euphorbiaceae by the absence of latex and laticifers. To test this long-standing assumption, we anatomically analysed 40 species in 10 genera, representing six of the nine subclades of Acalyphoideae s.s., to examine the presence of laticifers using leaf blade and petiole sections. Laticifers were observed in all the studied species and consisted of multinucleate, elongated cells with dense cytoplasm. They were articulated and branched in <i>Acalypha</i>, <i>Bia</i>, and <i>Dalechampia</i>; this was further confirmed by ontogenetic analyses in <i>Acalypha accedens</i>, <i>A. brasiliensis</i>, and <i>A. poiretii</i>. Histochemical tests revealed lipids, proteins, mucilage, and starch in laticifers. Our results demonstrate that laticifers are present and common in Acalyphoideae and thus more widespread in Euphorbiaceae than previously known. The scarcity of detailed anatomical studies, and the often imperceptible latex exudation of most Acalyphoideae, are probably the main reasons that have misled field botanists and systematists in the past.