Briquetiastrum : a new genus of Malvaceae and the redefinition of Briquetia

Bovini, M.G. 2015. Briquetiastrum: a new genus of Malvaceae and the redefinition of Briquetia. Anales Jard. Bot. Madrid 72(2): e022 A historical overview of the genus Briquetia, with an analysis of its circumscription conflicts and the proposal for a new genus, Briquetiastrum, based on new morphological studies and phytogeographical data were made. A taxonomic treatment and three new combinations from Briquetia to Briquetiastrum (Briquetiastrum inermis, B. spicatum and B. sonorae) are presented and Briquetiastrum sonorae is illustrated for the first time. Descriptions and a key to the treated species are included.


INTRODUCTION
The genus Briquetia Hochr., described by Hochreutiner (1902), has still a fragile and inconsistent circumscription.This characteristic is shared with other genera, such as Batesimalva Fryxell, Dirhamphis Krapov., Hochreutinera Krapov., Horsfordia A. Gray, Pseudabutilon R.E.Fries, and Wissadula Medik., which are morphologically very similar to it.A striking feature common to these genera is the fruit, in which the morphology of the calyx and mericarp, the presence or absence of endoglossum, and the number of seeds, frequently combine to define the taxon.Krapovickas (1970), Fryxell (1976Fryxell ( , 1997Fryxell ( , 2007)), and Bovini (2009Bovini ( , 2010)), commented on the morphology of some of these genera, analyzed their differences, and proposed new genera and species that are similar to Briquetia.
In spite of their efforts, the generic boundaries in this group are not clearly defined yet, due to the use of diagnostic fruit features that do not seem unambiguously associated to each one.Moreover, Fryxell & Stelly (1993) counted the chromosomes of some Malvaceae and concluded that species of Dirhamphis need to be revaluated, because their basic chromosome numbers differ and perhaps they may be not congeneric.Later, Tate & al. (2005) made a phylogenetic analysis of the genera of the tribe Malveae based on molecular data and concluded that they are geographically, chromosomally, and morphologically divided in several clades, and that the phylogeny with ITS markers with 14 generic alliances proposed initially by Bates (1968;Bates & Blanchard 1970) and later presented by Bayer & Kubitzki (2003) is artificial.This phylogeny identified a series of closely related genera of this tribe.(Batesimalva, Briquetia, Dirhamphis, Hochreutinera, Horsfordia, Pseudabutilon, and Wissadula), among which the results showed a close relationship between Briquetia, Dirhamphis, and Hochreutinera.
Based on the review of specimens from several herbaria, its morphological analysis, and literature review, the present study aims at establishing morphological limits for the ge nus Briquetia.It also aims at proposing a new genus of Malvaceae, named Briquetiastrum, which includes a group of species described by Fryxell (1976Fryxell ( , 1990) ) under Briquetia due to their floral characters in common, but which differ from those described in the type species of Briquetia.

MATERIAL AND METHODS
The present study was based on the analysis of collections of national and international herbaria: ARIZ, INPA, K, LL, MBM, NY, RB, US, (Thiers 2012), as well as fieldwork carried by the author.The criteria for typification followed McNeill & al. (2012), and morphological analysis under a stereoscopic microscope, and used a caliper to take the measurements.
The species were evaluated in their conservation status following the categories and criteria of IUCN (2001), and provided subsidies for defining species that should be protected.
For pollen analysis, flowers or flower buds from three samples of each species were used, except for Briquetiastrum inermis, whose material was removed from specimens deposited in the herbaria ARIZ, NY, and RB.Pollen grains were observed, analyzed, and photographed in a S.E.M Zeiss EVO-40 microscope, at the Research Institute of the Botanical Gardens of Rio de Janeiro, and the terminology adopted in the morphological description followed Barth & Melhem (1988).The map here presented was designed using the software package ArcGIS 9.3.

Intrageneric relationships
Briquetia was described as a monotypic genus in 1902, based on a specimen from Paraguay, B. ancylocarpa Hochr., which had one ovule per mericarp and two hook-shaped aristae located at the lower outer part of the mericarp.Later, Hassler (1905) established the combination Briquetia denudata (Nees & Mart.)Chodat & Hassl.for a species from Bahia (Brazil) that previously was described as belonging to the genus Sida L., and reported the new synonym B. ancylocarpa, which was described after S. denudata.
Literature reviews brought out many doubts about the true morphology of the genus.When Hochreutiner (1902) described Briquetia for the first time, he emphasized the presence of two small hooks in the lower part of the mericarps and the presence of one seed.However, what called the attention is the lack of endoglossum in the original description, which is a characteristic that frequently limits the current characterization of genus.
For decades, there were only a few studies about the genus; only Krapovickas (1970) and Fryxell (1976) provided taxonomic notes or proposed new species.According to Fryxell (1997), Briquetia comprised five species, among which only B. spicata (Kunth) Fryxell is broadly distributed in the Neotropics, whereas the other four species have a more restricted distribution, and are poorly known in terms of morphology.Fryxell (1997) also reported that the genus needs further studies, because as new species of Briquetia were described, their generic characteristics have been suppressed and currently there is no basic set of characters that separates the genus Briquetia from similar genera.
The proposal to differentiate the above mentioned genera is presented in Table 1 the morphological characteristics of similar genera, with the new morphological limits for Briquetia and the establishment of the new genus Briquetiastrum.
Geographical distribution: Briquetiastrum is a Neotropical genus.It occurs from Mexico to Brazil at the limit of the Tropic of Capricorn.In South America there are no records for Argentina, Chile, Paraguay, and Uruguay (Fig. 1).
Geographic distribution: Briquetiastrum inermis is known only from three samples of Mexico, two collected in the state of Chihuahua, and one collected in the state of Sinaloa.Based on the studied specimens, it occurs in arid areas.
Conservation status: There are no data on abundance or population size for this species.There is almost no information available on its environment and threats to its conservation.Date Deficient species.
Geographic distribution: Briquetiastrum sonorae occurs only in Mexico, where it is found in the Sonora desert in xeric shrubby forests; it is poorly represented in herbaria, probably due to its very restrict distribution.Its sympatric distribution is well delimited, with consistent morphological characteristics.
Conservation status: Occurs in protected areas and there is strong evidence of the rarity for this species.Its extent of occurrence (EOO) is smaller than 5,000 km² and this species can be considered EN B1b (i, ii, iv).
Anales del Jardín Botánico de Madrid 72( 2   Geographic distribution: Briquetia denudata occurs in Argentina, Paraguay, and Brazil.In the latter, occurs in the states of Bahia, Minas Gerais, Mato Grosso do Sul, and Paraná, in the Pantanal and Cerrado biomes. Conservation status: The species is poorly represented in collections and occurs in some already threatened localities, such as the Cerrado.In the state of Bahia, it was only found in the type collection.I infer that there has been a decline in the quality of its habitat and its EOO is smaller than 20,000 km².Briquetia denudata was considered VU B1ab (i, ii, iii).
With our new circumscription,the genus Briquetia becomes monotypic.It is characterized by the presence of two hook-shaped projections on the base of the mericarp, one seed per mericarp, and the lack of endoglossum.