First record of Voyria caerulea Aubl. (Gentianaceae), a mycoheterotrophic plant, in Maranhão state, northeastern Brazil

We report the first record of Voyria caerulea from the state of Maranhão, northeastern Brazil. A fertile specimen was collected in a gallery forest during the rainy season, within the boundaries of the municipality of São Raimundo das Mangabeiras. This find contributes to the knowledge on the micoheterotrophic flora of Maranhão and expands the geographic distribution of this species in Brazil. We also present a taxonomic description, illustrations, an occurrence map of the newly found population, and an identification key for all the species of Voyria that occur in Maranhão.


Introduction
Gentianaceae Juss. is composed by 99 genera and approximately 1,700 species that are widely distributed across the globe, except in Antarctica.In Brazil, the family is currently represented by approximately 31 genera and 122 species (BFG 2015).Although most plants in the family are autotrophic, mycoheterotrophy has been reported for 30 species, 18 of which belong to Voyria Aubl.(Maas and Ruyters 1986, Struwe et al. 2002, Gentian Research Network 2011, Merckx et al. 2013a, b).Voyria species are achlorophyllous, fully mycoheterotrophic plants; that is, they have lost the ability to perform photosynthesis and completely depend on symbiotic associations with fungi to obtain carbon during their entire life cycle (Merckx et al. 2013a, b).They are small, delicate herbs with yellowish, orange, reddish, or whitish stems and with leaves reduced in size (Maas and Ruyters 1986, Merckx et al. 2010, 2013a, b).They are small in size, typically are visible only when their brightly colored (yellowish, blue, or whitish) flowers bloom, and rarely form large populations; for these reasons they are difficult to observe in the field and are not frequent in herbaria (Struwe et al. 2002, Merckx et al. 2010, 2013a, b, Courty et al. 2011, Gentian Research Network 2011).
A specimen identified as Voyria caerulea Aubl.was collected during fieldwork in Maranhão state, in which until recently, only 4 species of Voyria had been reported: V. aurantiaca Splitg., V. flavescens Griseb., V. spruceana Benth., and V. tenella Guild.ex.Hook.(Voyria in Brazilian Flora 2018, Koch and Araújo-Silva 2014).We report the occurrence of this rare species from Maranhão, Brazil, and present an identification key to the species of Voyria known to occur in in this state.

Methods
We collected Voyria caerulea Aubl.during field expeditions in February 2017 within the boundaries of the municipality of São Raimundo das Mangabeiras, central region of Maranhão state, Brazil.Plants were found on the banks of the Gameleira Creek, a tributary of the Itapecuru River, in the Itapecuru basin, in a gallery forest adjacent to an area of Cerrado (Brazilian savanna) (Fig. 1).This area is threatened by fires caused by agricultural activities during the dry season from April to September (Silva- Júnior et al. 2018).
Plants were photographed with a digital camera and a Tecnal ® ME-SZ stereoscopic microscope coupled to a Carl Zeiss ® , AxioCam ERc5s digital camera, and the geographic coordinates of the site were obtained using a Garmin eTrex ® 30x GPS receiver.
Collected specimens were herborized following the Technical Manual of the Brazilian Vegetation (IBGE 2012).To avoid a drastic reduction of the population, only 2 out of the 3 inflorescences observed in the field were collected.The exsiccata was incorporated into the herbarium MAR, located in the Department of Biology of the Federal University of Maranhão, São Luís, Maranhão, Brazil (acronym according to Thiers 2018).Specific literature was used to identify the specimens (Maas and Ruyters 1986, Franke 2002, Maas and Maas 2005, Melo et al. 2010, Gentian Research Network 2011, Melo and Alves 2013), and comparisons with specimens identified by experts at CEPEC, HUEFS, HURB, INPA, JPB, MO, NY, and P (acronyms according to Thiers 2018).The geographic distribution of this species is from the online databases Brazilian Flora (2018), Tropicos (2018) and SpeciesLink (2018).The map was created in QGIS v. 2.14 Essen 4 (QGIS Development Team), using SIRGAS 2000.Figures of specimens were edited using Photoshop ® CS5 v. 12.0 (Adobe ® Systems) were used to map and illustrate this species, respectively.

Discussion
Voyria caerulea occurs in Guyana, French Guiana, Suriname, Venezuela, and Brazil where it is found in areas of the Amazon Forest, Cerrado, and Atlantic Forest, in the states of Amazonas, Pará, Paraíba, Pernambuco, Sergipe, Bahia, and Mato Grosso (Maas and Ruyters 1986, Gentian Research Network 2011, Tropicos 2018, Brazilian Flora 2018).According to the information available in Specieslink ( 2018), the three sites with previous records of V. caerulea closest to this new record in the Maranhão state (Fig. 1) are: 1-) Jintituba Serra, municipality of Flexeiras, Alagoas state, northeastern Brazil, located 1,096 km of distance; 2-) Barra dos Garças, Mato Grosso state, Midwestern Brazil, located at 1,181 km of distance and 3-) Lageira, Pará state, northern Brazil, located 1,038 km of distance.The loss of habitats caused by fire and deforestation caused by agriculture activities near the new occurrence of V. caerulea suggests that this species, as many others inhabiting the Cerrado, may be threatened.In fact, fire and deforestation are associated with the loss of biodiversity in the Cerrado (Abreu et al. 2017).
Our observations in the field point to a the low population density of V. caerulea: only 1 individual was found after we walked approximatetly 500 m along the banks of the creek associated with the studied gallery forest.This is confirmed by the pollination study carried out by Hentrich et al. (2013) in French Guiana where they recorded only 17 individuals of V. caerulea along about 20 km of trails.Hentrich et al. ( 2013) also reported that V. caerulea was visited only once by a butterfly in 6 days of field observations and that its seeds are dispersed concentrically and/or by rodents.Thus, it is a rarely observed, pollinated and collected species, making our new record important.
The rarity of V. caerulea at the new site agrees with what is known for this species and others belonging to genus Voyria.In the field, they are clustered in small populations with only a few individuals (Maas andRuyters 1986, Struwe et al. 2002).Mycoheterotrophic plants, such as V. caerulea, are not very visible and rare, and therefore, the distributions of such plants may be underestimated.Voyria caerulea may also occur in states neighboring Maranhão, where its is still unreported, and additional efforts to document mycoheterotrophic species, such as V. caerulea, are needed.

Figure 1 .
Figure 1.Collection site of Voyria caerulea Aubl. in Maranhão state, northeastern Brazil.= new record.= previous collections of Voyria caerulea closer to the new record.

Figure 2 .
Figure 2. Voyria caerulea Aubl.(A.W.C.Ferreira et al. 251, MAR 9284).A. Flower in frontal view.B. Flower in lateral view.C. Detail of a leaf from a dried herbarium specimen.D. Flowering plants in their habitat.E. Detail of a flowering plant in a dried herbarium specimen.