New record of Euphorbia thymifolia L. (Euphorbiaceae) from the state of Acre, Brazil

Euphorbia thymifolia (Euphorbiaceae) is a prostrate herb, distinguished from similar species by the combination of serrate leaf margin, puberulous ovary/fruit with capitate styles and pedicel not accrescent in fruit, splitting the involucre of the cyathia during maturation. In this paper we present the first record of E. thymifolia for the state of Acre, in Alto Juruá region, municipality of Cruzeiro do Sul, in a residential sidewalk crack habitat (07°36′58″S, 072°41′14.12″W WGS84). We also comment on its habitat and distribution, and include comparisons with commonly misidentified related species.


Introduction
Euphorbiaceae is one of the most expressive flora families in the Brazilian Amazon (BFG 2015). Ricardo Secco's studies of this family have stood out since the eighties (Secco 1987, 1990Costa et al. 2018;among others). Such studies found that the Amazon constitutes a diversity center of many genera Secco 2011, 2012;Souza and Secco 2014), some of which are endemic (e.g., Micrandropsis W.A. Rodrigues and Sandwithia Lanj.) and others have few specimens available in herbaria (e.g., Angostylis Benth. and Astrococcus Benth.). However, most of these studies have prioritized trees and lianas (Souza et al. 2014;Secco and Bigio 2017;Costa et al. 2018;Secco et al. 2019), and little attention has been given to herbaceous plants, even though they are common. Such conduct is also observed in other families in the mentioned bioma (Souza et al. 2020).
For instance, in the state of Amazonas, 54 species and 33 genera of Euphorbiaceae were recorded (Ribeiro et al. 1999), among which only four genera and eight species are herbaceous plants. For the state of Acre, the results were not different. Out of 37 genera and 98 species recorded, four genera and seven species refer to herbs (Daly and Silveira 2008;Medeiros et al. 2014).
In this context, the genus Euphorbia L. stands out, as it is the most diverse genus of Euphorbiaceae, with approximately 2,000 species, occurring in tropics and subtropics (Webster 2014). Most of its representatives have herbaceous habits, and its ruderal species are common in the Amazon. However, the local records of such species are rare and old, and many of them have been misidentified (Ribeiro et al. 1999). Such is the case of Euphorbia thymifolia L., which has been mistaken for E. prostrata Aiton and E. hyssopifolia L., among others (Silva et al. 2014).
From Acre state, Daly and Silveira (2008)  For E. capitellata, the collection (M. Urquia 188) referred to by Daly and Silveira (2008) was not found in virtual herbaria. Therefore, it was not possible to examine it. However, we strongly believe that this represents a misidentification, as E. capitellata only occurs in the southern USA and in northern Mexico (Yang 2014).
In this paper we present a new record of Euphorbia from Acre state. It is Euphorbia thymifolia, a ruderal plant of herbaceous habit, collected in the Alto Juruá region in the westernmost area of Brazil.

Methods
The botanical material was collected in sidewalk crack, near the residence of the first author, in Formoso, municipality of Cruzeiro do Sul (07°36′58″S, 072°41′14″W, WGS84), as part of the Project Flora do Alto Juruá. The identification of the species was based on the taxonomic treatment of Euphorbia for the state of São Paulo (Silva et al. 2014), which includes all ruderal species found in Brazil. The identification was also made by comparison with images and data available via Tropicos.org (2020), SpeciesLink (2020), and Flora do Brasil (2020). The specimens were deposited in the Campus Floresta Herbarium (CFCZS) of the Universidade Federal do Acre according to usual procedures for Plant Systematics (Bridson and Forman 1998). Herbaria acronyms follow the standards of Holmgreen et al. (1990).
Given the common misidentification of specimens of Euphorbia thymifolia, the geographical distribution of Euphorbia thymifolia in Brazil ( Fig. 1) is based on occurrences gathered only from selected herbaria (ALCB, ASE, BHCB, BOTY, CEN, CEPEC, CESJ, CGMS, ESA, HRCB, HUEFS, HUEM, IAC, JPB, MAC, MBM, PEUFR, R, RB, SP, SPF, UB, UEC, UFP, UFRN) visited by the authors of this paper, available in Reflora virtual herbarium (Flora do Brasil 2020) and the Species-Link database (SpeciesLink 2020). When coordinates could not be retrieved directly from these databases, we searched for approximate coordinates in Google Maps. We provided a complete list of vouchers included for the distribution map (Table 1).
Among the specimens analyzed, one recorded for the state of Amazonas attracted our attention due to the indication on its label of latex use by the Makú people, in the Uneiuxi Indigenous Land, for the purpose of curing eye infection (US 2708630). The potential of latex from E. thymifolia seems to be confirmed, as laboratory tests showed its efficacy against the action of fungi and bacteria (Hussain et al. 2014). There are other indications of the plant in traditional medicine, with reported features like laxative, aromatic, sedation, blood purification, anti-viral, anti-helminthic, anti-inflammatory, anti-spasmodic, and diuretic properties (Kainsa and Singh 2016;Muthumani et al. 2016).
The record of Euphorbia thymifolia for the first time for Acre state revealed the need for further collection efforts in the Northern region, not only of such species, but also of all the genus, whose specimens deposited in the reference herbaria are rare and old. Before this record, E. thymifolia was only known from the states of Amapá, Amazonas, and Pará (Lima et al. 1995;Ribeiro et al. 1999;Silva et al. 2014;Flora do Brasil 2020). This new record enhances the knowledge of the local flora and confirms gaps concerning ruderal species.