Original Paper Flora of Ceará, Brazil: Cabombaceae

The present study analyzed taxa of the family Cabombaceae occurring in the state of Ceará. Only Cabomba species was represented, with C. aquatica and C. haynesii recorded in the state. Populations occur in permanent and temporary lentic environments, such as lagoons and shores of lotic systems. This work presents taxon identification keys, morphological descriptions, illustrations, comments and geographic distribution data.


Introduction
The aquatic environments in the state of Ceará are temporary or permanent, with significant species richness, including representatives of Alismataceae with 13 species (Matias & Souza 2011), Araceae with 7 spp. (Andrade et al. 2013), Hydrocharitaceae with 9 spp. (Matias et al. 2017) and Pontederiaceae with 10 spp. (Souza et al. 2018), in addition to the marine phanerogams that are represented by 3 species (Matias et al. 2017). Eudicotyledoneae include approximately 130 aquatic taxa present in the state. Among the basal groups, the order Nymphaeales has only Nymphaeaceae and Cabombaceae with representatives in Brazil, with seven species of Nymphaea described for the Ceará state  and with an indication for the occurrence of 3 species of Cabomba (Pellegrini 2020).
In natural environments, populations of Cabomba cover tropical and warm temperate climate zones of the Neotropics, in lentic or lotic, alkaline or acidic environments, and whose seasonality does not imply a limiting factor since the populations are adapted to conditions of water fluctuation and feature rapid growth during the rainy season (Ørgaard 1991). Cabomba species can develop in eutrophic, aquatic environments (Huang et al. 2017) as well as contaminated waters; therefore, they are commonly studied for potential use in phytoremediation systems of pesticides and heavy metals (Olette et al. 2008). Furthermore, Cabomba populations are reported as biotic agents causing changes in aquatic communities in regions of North America where their introduction has occurred (Hogsden et al. 2007) and, on the Australian continent, control measures have been employed in vulnerable environments (Biosecurity Act 2014).
Cabombaceae has been positioned in a monophyletic group with Nymphaeaceae, and apomorphies of Cabombaceae include alternate phyllotaxis of floating leaves, placement of submerged leaves and presence of hairs on emergent surfaces of the leaves or petioles (Taylor 2008). Pollination systems are diverse in Cabombaceae, with fly pollination present in Cabomba species, while anemophily arose recently in Brasenia; this implies the development of an apomorphic stylar extension, which in Brasenia became greatly elongated to produce a much larger stigmatic surface, in addition to different patterns of pollentube development and fertilization (Taylor & Williams 2009). Bee pollination was reported by Vogel (1998).
The species of Cabombaceae can be identified by stems with dimorphic leaves characterized by floating, entire, peltate leaves and submerged, divided leaves with linear lobes. The trimerous perianth, monocolpate pollen, apocarpous gynoecium and two, connate cotyledons are also diagnostic characters of Cabombaceae (Simpson 2010).
Five species of Cabombaceae occur in Brazil: C. aquatica Aubl., C. caroliniana A. Gray, C. furcata Schult. & Schult., C. haynesii Wiersema and C. schwartzii Rataj (Pellegrini 2019). All species ranging from North through South of Brazil, except C. schwartzii that is an endemic species from Amazon region (Pellegrini 2019). There are floristic surveys of Rio de Janeiro (Correia & Bove 2017), Bahia (Lima et al. 2012), São Paulo (Feres & Amaral 2003), and the State with the highest number of species is Bahia (4 spp.). This work aims for a floristic study of Cabombaceae of Ceará state in order to update geographic distribution and to provide morphological and taxonomic data to improve the knowledge about the Brazilian flora.

Materials and Methods
For the floristic survey, we collected information on samples collected from 2000 to 2018 and deposited in the EAC Herbarium (Prisco Bezerra Herbarium) as well as from records of the speciesLink database (CRIA 2001, ongoing) and the Reflora-Virtual Herbarium (2018). Specialized journal articles, such as Ørgaard (1991) and Jacobsen & Ørgaard (1989) were consulted to identify the botanical specimens. The description of Cabombaceae as a whole follows Wiersema (1997) and genus follows Fassett (1953) and Ørgaard (1991). The scientific plant names are in conformity with the International Plant Names Index -IPNI (continuously updated). The morphological terms follow Radford et al. (1974). The geographic distribution map was elaborated using QGIS 3.2.3 based on data of samples from wetlands located within the coordinates 02º46'-07º52'S and 37º14'-41º26'W (IPECE 2017).
Cabombaceae is represented in Brazil by aquatic herbs of the genera Cabomba Aubl. (BFG 2015(BFG , 2018. In addition, the fossil taxon Pluricarpellatia peltata B. Mohr, Bernardes-de-Oliveira & David W. Taylor has been found in southern Ceará in the Crato Formation (Mohr et al. 2008). Brasenia and Cabomba diverged in the Cretaceous Period about 31-10 mya (Bell et al. 2010) or 109-52 mya (Wikström et al. 2001), while Pluricarpellatia is estimated to have lived 115 mya (Mohr et al. 2008). The monotypic genus Brasenia (B. schreberi J.F.Gmel.) is spread across temperate and tropical regions of Africa, Asia, Australia and North America, while Cabomba species can be found throughout the Neotropics (Cook 1996). Only one genus and total five species and two varieties in the Brazilian flora and four taxa are indicated to the Brazilian Northeast (Pellegrini 2019).