Flora of Anacardium (Anacardiaceae) in the state of Pará, Brazil

This study presents a taxonomic treatment of Anacardium for the state of Pará (Brazil), based on the analysis of specimens from herbaria (CEN, ESA, IAN, INPA, MBM, MFS, MG, RB, UB, and UEC), material collected in the field, and images of specimens from virtual databases. Species identifications were confirmed by consultation of protologues and types or images of types. A morphoanatomical analysis of the leaves of Anacardium was conducted to support taxonomic characterizations. Descriptions, plates, a distribution map, and an identification key for the species of Anacardium occurring in Pará ( A . amapaense , A . giganteum , A . humile , A . microsepalum , A . occidentale , and A . spruceanum ) are provided.


Introduction
Anacardiaceae is one of the nine families of the order Sapindales (APG IV 2016) and is divided into the subfamilies Anacardioideae and Spondioideae (Pell et al. 2004;Mitchell et al. 2006;Wannan 2006;Pell et al. 2011).The family has a mainly tropical and subtropical distribution and comprises about 80 genera and 800 species (Mitchell & Mori 1987;Mitchell 1992;Pell et al. 2011).In Brazil, Anacardiaceae is represented by 15 genera and 64 species (19 endemic), with higher concentrations of species in the Atlantic Forest (32 species) and the Amazon (26 species) (Silva-Luz et al. 2020).
Table 1 -Voucher information of Anacardium species used for morphoanatomical analysis.
Anacardium L. is one of the best-known genera of Anacardiaceae (Mitchell & Mori 1987;Barros & Crisóstomo 1995;Garcia 2009).According to the most recent taxonomic revision of the genus, it comprises 11 species (Mitchell & Mori 1987), nine of which occur in Brazil (Mitchell & Mori 1987;Mitchell 1992;Silva-Luz et al. 2020).Anacardium has a neotropical distribution with a primary center of diversity in the Amazon (Mitchell & Mori 1987).
Although Anacardium is a well-studied genus, the identification of some species remains complex.In the Amazon region, the flowering specimens are rare cycles of some of its species are not frequent, beingand it is difficult to identify sterile individuals, in some cases, due to overlapping morphological characters.The state of Pará, therefore, is an important study area since it encompasses most of the species of Anacardium found in the Amazon (Pereira et al. 2014).Thus, in order to improve the knowledge of the genus, we provide a taxonomic treatment of the species of Anacardium that occur in the state of Pará, Brazil.

Anatomical analysis
Anatomical study was based on the analysis of dried leaves obtained from herbarium vouchers.For purposes of comparison, we also analyzed the Amazonian species Anacardium parvifolium Ducke, which does not occur in the state of Pará.Leaf blades were extracted from the fourth and fifth nodes of three specimens of each species (Tab.1).The leaf fragments were rehydrated in boiling distilled water and treated with 2% potassium hydroxide (KOH) until they submerged (Smith & Smith 1942).These samples were then isolated, dehydrated in an ethyl series up to 70% (Johansen 1940), embedded in methacrylate (Leica Historesina, Germany) (Meira & Martins 2003), and sectioned with a rotary microtome (Leica RM2245, Germany).The sections (transverse, 5-6 µm thick) were stained with toluidine blue at pH 4.0 (O'Brien & McCully 1981) for structural characterization.
Rodriguésia 72: e02142020.2021 Photomicrographs were obtained using a digital camera (Zeiss AxioCam ICc5, Germany) coupled to a microscope (Zeiss Axio Scope.A1, Germany).Other portions of the samples were also critical-point dried, sputter coated with a thin layer of gold (Robards 1978), and electromicrographed using a scanning electron microscope (Zeiss Sigma VP, Germany).

Taxonomic treatment
Taxonomic study was based on the analysis of collections of the herbaria CEN, ESA, IAN, INPA, MBM, MFS, MG, RB, UB, and UEC [acronyms according to Thiers (continuously updated)], specimens collected by us, and images of herbarium vouchers from the databases INCT -Virtual Herbarium of Flora and Fungi (speciesLink 2020) and Reflora -Virtual Herbarium (Reflora 2020).Collected material was incorporated into the herbaria MFS and UEC.Species identifications were confirmed through the analysis of protologues and types or images of types available at the JSTOR Global Plants website (Ithaka 2020).
Structures were analyzed and described under a stereomicroscope and measured using a digital caliper and graph paper.Information on leaf color is based on dried material.The terminology used follows Radford et al. (1974), Mitchell & Mori (1987), Mitchell (1992) (especially for the orifices located in the axils of secondary veins on the abaxial surface), Pirani (2003), and Lacchia et al. (2016).When necessary, descriptions were complemented with data from additional material.Also, we included in the taxonomic descriptions the information obtained and confirmed by the anatomical analysis.Data on distribution, habitat, and phenology were obtained from herbarium vouchers, literature, and field notes.Distribution maps were created using ArcGis 10.1 (ESRI 2012).
The structures analyzed here consist of glandular trichomes organized in groups.They may be found in depressions (Anacardium giganteum,A. microsepalum,A. occidentale, or cavities (A.amapaense and A. spruceanum) (Fig. 1c; h-j) located in the axils of secondary veins on the abaxial surface.The depressions have a rounded shape and a shallow orifice in the central region, while cavities have a linear or narrowly lanceolate shape and a deep, pit-like orifice (Mitchell & Mori 1987;Mitchell 1992).The cells below the trichomes have a polygonal form, are thick-walled, and may compose one or more layers (Fig. 1dm).The glandular trichomes are multicellular and multiseriate with a unicellular stalk and a secretory head that is elongated in the anticlinal direction.The number of cell series ranges from two to eight, while the number of cells in each series ranges from two to six (Fig. 1j-l).In view of the anatomical similarities between the structures observed by us for Anacardium amapaense, A. giganteum, A. microsepalum, A. occidentale, A. parvifolium, and A. spruceanum, and the extrafloral nectaries (EFNs) described by Lacchia et al. (2016) for A. humile, we believe that what we observed are also EFNs.
The polygonal cells below the trichomes are similar to those impregnated with suberin that surround the tissue of many secretory structures in other plants (Paiva & Machado 2005;Paiva et al. 2007;Filgueira et al. 2016).According to Lüttge (1971), this suberin impregnation of cell walls could block the return of exudates to the inner tissues.Thus, we believe that the polygonal cells below the trichomes of the analyzed species could be contributing to the storage of secretion (possibly nectar) by these structures.

Figure 1
Figure 1 -a-c.Front view of the axils of secondary veins on the abaxial surface of leaves under SEM -a.Anacardium microsepalum; b. A. occidentale; c. A. spruceanum.d-i.cross sections of leaves showing glandular trichomes within cavities or depressions located in the axils of secondary veins on the abaxial surface -d.trichomes found within depression in A. giganteum; e. trichomes found within depression in A. microsepalum; f. trichomes found within depression in A. occidentale; g. trichomes found within depression in A. parvifolium; h.trichomes found within cavity in A. amapaense; i. trichomes found within cavity in A. spruceanum.j-l.detail of glandular trichomes -j-k. A. giganteum; l. A. occidentale.

Figure 2
Figure 2 -a-d.Anacardium amapaense -a.flowering branch; b. detail of cavity with glandular trichomes in the axil of a secondary vein on the abaxial leaf surface; c. flower; d. petal.e-i. A. giganteum -e.flowering branch; f. detail of depression with glandular trichomes in the axil of a secondary vein on the abaxial leaf surface; g. flower; h.petal; i. fruit.j-n. A. humile -j.flowering branch; k. detail of depression with glandular trichomes in the axil of a secondary vein on the abaxial leaf surface; l. flower; m. petal; n. fruit.o-s. A. microsepalum -o.flowering branch; p. detail of depression with glandular trichomes in the axil of a secondary vein on the abaxial leaf surface; q. flower; r. petal; s. fruit.t-x. A. occidentale -t.flowering branch; u. detail of depression with glandular trichomes in the axil of a secondary vein on the abaxial leaf surface; v. flower; w. petal; x. fruit.y-c'. A. spruceanum -y.flowering branch; z. detail of cavity with glandular trichomes in the axil of a secondary vein on the abaxial leaf surface; a'.flower; b'.petal; c'.fruit.(a-d.L.C.B. Lobato et al. 2568; e-h.J.M. Pires & N.T. Silva 11073; i. W.A. Archer 7813; j-k.N.T. Silva 719; l-n. A. Gély 369; o-r.P. Cavalcante 1125; s.J.G. de Carvalho-Sobrinho et al. 1504; t-u.O.C. Nascimento et al. 898; v-w.A.E.S. Rocha et al. 297; x.O.C. do Nascimento BPM215; y-b'.N.T. da Silva 5137; c'.M.R. Santos 683).
Figure 3 -a-b.Distribution map of Anacardium in the state of Pará, Brazil -a.Brazil; b. distribution of Anacardium in Pará.