Morphological and anatomical evidence support a new wild cassava: Manihot fallax (Crotonoideae, Euphorbiaceae), from Mato Grosso, Brazil

Abstract During the preparation of the taxonomic treatment of Manihot in the Midwest Region of Brazil, a new species was found. Manihot fallax M.J. Silva & L.S. Inocencio is described, illustrated and morphologically compared with similar simple-leaved species. The conservation status, geographic distribution (including map), ecology, phenology and notes about leaf anatomy of the new species are given. The synonymisation of M. robusta M. Mend. & T. B. Cavalc. under M. attenuata Müll. Arg. and lectotypes for M. attenuata and M. brachystachys Pax & K. Hoffm are also proposed. An emended description of M. attenuata is proposed as the original description is incomplete as it lacks information on the pistillate flowers, fruits and seeds.


Introduction
The taxonomy of Manihot was studied by Rogers and Appan (1973), who recognised 98 species distributed into 19 sections. The genus is monophyletic and has a complex taxonomy (Duputié et al. 2011, Silva 2014. In Brazil, it is represented by over 80 species, especially growing in the Cerrado region, in rocky fields and grasslands (Silva 2014.
Despite the revision of Manihot (Rogers and Appan 1973), taxonomic studies about this genus in Brazil are scarce. Manihot is cited in floristic surveys of Euphorbiaceae (Cordeiro 1992, Sátiro andRoque 2008) or as an isolated genus (Allem 1997, Rodrigues 2007, Carmo-Júnior et al. 2013, Orlandini and Lima 2014. In the last four years, a number of species of Manihot have been described in Brazil in the coastal sand plains of the state of Sergipe (Martins et al. 2011), in the semi-arid region of the state of Bahia ) and in Cerrado sensu lato of the state of Goiás (e.g. Mendoza et al. 2015, 2017, Silva 2014, 2015, Silva and Sodré 2014. Considering the species of Manihot present in the Midwest Region of Brazil, the knowledge about the genus is scarce mainly in the states of Mato Grosso and Mato Grosso do Sul, where BFG (2015) reported 17 and 6 species respectively. However, taking into consideration that the flora of these states is relatively poorly known, that Manihot has its main diversity centre in the Brazilian Cerrado and also that these states have their areas covered predominantly by Cerrado vegetation, it is plausible to conclude that the number of species of the genus has been underestimated in Mato Grosso and Mato Grosso do Sul.
During the preparation of the taxonomic treatment of Manihot in the Midwest Region of Brazil, some collections were found from Serra Azul, Serra do Roncador, Serra do Taquaral and neighbouring areas in the state of Mato Grosso, which could not be assigned to any known species. One of these species, with entire and unlobed leaves and habit slender and virgate, is hereby illustrated, described as new and designated as M. fallax. The new species is compared with M. attenuata Müll. Arg. and M. weddelliana Baill., the taxa most morphologically similar to it and its phenology, conservation status and geographic distribution are also presented. The leaf anatomy of the new species and the species most morphologicaly similar to it were also compared because leaf anatomy constitutes an important tool for delimiting taxa in Manihot (e.g. Vannucci 1982, Cunha Neto et al. 2014, Cunha Neto et al. 2017and Graciano-Ribeiro et al. 2016. Additionally, as part of these studies on Manihot of the Cerrado flora, M. robusta as a synonym of M. attenuata Müll. Arg. is proposed and M. attenuata and M. brachystachys Pax & K. Hoffm are lectotypified. An emended description of M. attenuata is provided, as the original description is incomplete as it lacks information on the pistillate flowers, fruits and seeds.

Morphological and taxonomic studies
The morphological description of the new species is based on field observations, conducted by the authors during expeditions to the state of Mato Grosso and on morphological analyses of 34 collections from the authors and 10 collections from herbaria (UFMT/ICLMA and IAC). The emended description of Manihot attenuata and the nomenclatural revision for all taxa associated with it, resulted from analysis of all pro-tologues, type and historical collections (17 exsiccatae) of the same and also of extensive field work in their areas of occurrence, as well as analyses of 30 collections from herbaria (BR, CEN, F, G, HRCB, HUEFS, IBGE, K, MG, MO, NY, P, RB, S, SP, UB  and UFG). The terminology used in the description of both species is based on specific literature such as Pohl (1827), Pax (1910) and Rogers and Appan (1973); the last was employed mainly for the inflorescence types and venation pattern. All the samples used in the description of the new species, including the holotype, were deposited in the UFG herbarium and the isotypes will be sent to K, NY and MO. The acronyms of herbaria previously cited follow Thiers (2017, continuously updated) The conservation assessment of both the species was based on field observations and applying the IUCN Red List Categories and Criteria (IUCN 2014). The geographic distribution map was made using the software QGIS (Quantum GIS Development Team) version 2.8.1, which was used for the geographic coordinates obtained both during the collection expeditions and from the labels of the collections examined. The extent of occurrence (EOO) was calculated with the Geospatial Conservation Assessment Tool (GeoCAT -http://geocat.kew.org), (Bachman et al. 2011).

Manihot fallax
Distribution and ecology. Manihot fallax appears endemic to the state of Mato Grosso (Fig. 3), where it grows in Cerrado sensu stricto on flat or slope areas and also in grasslands, on clayey and sandy soils, between 385 m and 642 m elevation.
Phenology. The species has been collected with flowers and fruits from October to March.
Etymology. The specific Latin epithet "fallax" refers to deceptive and was chosen due to the false similarity of the new species to M. attenuata and M. weddelliana.
Discussion. Manihot fallax stands out from the other species of the genus with entire and unlobed leaves (Silva 2015) by its shrubby, slender, virgate habit up to 1.9 m tall, leaves ascendant and in a spiral arrangement along the branches. It morphologically resembles M. weddelliana and M. attenuata, especially the latter, in the aspect of the leaves, racemes conspicuously pedunculate, bracts of flowers of both sexes showy and foliaceous and calyx internally shortly tomentose. However, M. fallax differs from M. weddelliana in its shrubby, slender and virgate habit (vs. subshrub up to 0.5 cm tall in M. weddelliana), leaves without repand margins (vs. leaves with repand margins) and bracts of both staminate and pistillate flowers ovate, with margins entire and apex acute or obtuse (vs. widely elliptic, with margins very serrated and apex conspicuously acuminate). The combination of the characters listed in table below serve to differentiate M. attenuata from M. fallax.
Regarding leaf anatomical features, M. fallax differs from M. attenuata in having the vascular cylinder with arch-shaped collateral vascular bundles surrounded by pericyclic fibres in the midvein (Fig. 4A), uniseriate epidermis in the median portion of both surfaces of the leaf blade (Fig. 4B), at the edge (Fig. 4C) and petiole with collateral vascular bundles discontinuous in the vascular cylinder (Fig. 4N). In M. attenuata, the vascular cylinder has collateral vascular bundles in a flattened arc, not surrounded by pericyclic fibres in the midvein (Fig. 4D), epidermal cells without papillae in the median portion of the abaxial surface of the leaf blade (Fig. 4E), but with druses in the  protoplast (Fig. 4E, F), as well as petiole with collateral vascular bundles continuous in the vascular cylinder (Fig. 4O). Both M. fallax and M. attenuata have midveins with angular collenchyma on both surfaces, ground parenchyma surrounding the vascular cylinder (Fig. 4A, D, H), isobilateral mesophyll (Fig. 4B, E), edges with annular collenchyma (Fig. 4C), parenchymatic sheath surrounding the secondary veins towards the epidermal cells on both surfaces of the leaf blade (Fig. 4I) and other veins without sheath (Fig. 4J). Laticifers are also found in both species distributed along the phloem cells in the midvein, petiole and median portion of the leaf blade (Fig. 4G). Additionally, the petiole has epidermal cells and cortex similar to those of the midvein (Fig. 4N, O). The stomata are paracytic in both species (Fig. 4K), evenly distributed on the abaxial surface of the leaf blade (Fig. 4L) and in a parallel and continuous band on each side of the midrib (Fig. 4M). Due to the stomatal pattern, both species have amphistomatic leaves.

Manihot attenuata
Morphological relationships and characterisation. Manihot attenuata is easily recognised by its shrub habit; erect or decumbent habit; large leaves (17.5-24 × 4-4.5 cm) that are purplish; sparsely serrate, persistent stipules; bracts and bracteoles of both staminate and pistillate flowers widely ovate, pubescent externally and acuminate at the apex; usually pendent inflorescences; and pubescent stigmatic branches. It is morphologically similar to M. fallax. However, it differs by the set of characters cited in Table 1 and also according the anatomical characters previously discussed.
Distribution and ecology. A species endemic to the northern portion of the state of Goiás, Chapada dos Veadeiros and neighbouring regions (municipalities of Niquelândia and Minaçu) (Fig. 3). It grows in cerrado rupestre, cerrado sensu stricto, near to rocky outcrops and in rocky fields, in flat sites, slopes or hilltops on clay-sandy soils, or in rock cracks, at altitudes from 440 and 1477 metres. Phenology. The species has been collected with flowers from November to March, with the flowers more common from September to December and with fruits from December to March.
Conservation Status. Manihot attenuata is here classified as Vulnerable (VU) according to the IUCN Red List Categories and Criteria (IUCN 2014) because it has an extent of occurrence of ca. 9850 km 2 . However, the species has populations with more 20 individuals and it grows in environments inappropriate for farming and habitations, as well as in protected areas such as the Chapada dos Veadeiros National Park.
Typification. Müller (1874) described M. attenuata in Flora Brasiliensis based on Burchell 7865 from Goiás state. Pax (1910) recognised M. attenuata as a good species without comment about its typification and established M. brachystachys. Rogers and Appan (1973) subordinated M. brachystachys Pax & K. Hoffm. as a synonym of M. attenuata without comment or typification of the latter. Analysing all type collections of both species confirmed that both species need to be lectotypified. The collection Burchell 7865 (Fig. 7) deposited in the herbarium K (K000600418) as lectotype of M. attenuata was designated here because it complies with the protologue and has flowers. Based on this same principle, the collection Glaziou 21126 at P (P04786133) was proposed as a lectotype of M. brachystachys; isolectotypes are BR (BR0000005101320), G (G00441911), K (K000600417), P (P04786134, P04786135) and S (S-R-9076). M. brachystachys was also recognised as a synonym for M. attenuata because the characters used by Pax (1910) to differentiate them (e.g. leaf type, habit, fusion of floral parts) overlap and are variable within populations.
Recently, Mendoza et al. (2015) published M. robusta as a new species from Chapada dos Veadeiros region in Goiás state. Reviewing all collections used by the authors in the description of M. robusta, based on the images provided by them and the characters cited to differentiate M. robusta from M. attenuata (e.g. habit and aspect of growth, secondary vein numbers, inflorescence position and numbers, bract shape and length), it is concluded that the characters cited by the authors overlap and are variable within populations. Furthermore, all collections of M. robusta are from the same location as the type of M. attenuata. It is therefore considered that M. robusta is a synonym of M. attenuata.