Poaceae: an Overview with Reference to Brazil Poaceae: Uma Visão Geral Com Referência Ao Brasil
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Rodriguésia 63(1): 089-100. 2012 http://rodriguesia.jbrj.gov.br Poaceae: an overview with reference to Brazil Poaceae: uma visão geral com referência ao Brasil Hilda Maria Longhi-Wagner1,2 Abstract A summary of the classification of Poaceae into subfamilies according to different proposals is provided, as well as data on morphology and chorology of grasses, especially those that occur in Brazil. Key words: Gramineae, classification, morphology, geographical distribution, Brazil. Resumo É fornecido um sumário da classificação de Poaceae em subfamílias, de acordo com diferentes propostas, bem como dados sobre a morfologia e corologia de gramíneas, especialmente daquelas ocorrentes no Brasil. Palavras-chave: Gramineae, classificação, morfologia, distribuição geográfica, Brasil. Introduction Classification in subfamilies and The family Poaceae (Gramineae) encompasses its relationship with morphology approximately 800 genera and 10,000 species and chorology (Watson & Dallwitz 1992), which predominate in the Several classification systems of Poaceae have flora and physiognomy of open vegetations all over been proposed, based mainly on the morphology the world. The economic importance of this family of the spikelets. Two large groups were accepted: is unquestionable for it has many different types of (1) spikelets with two anthecia (see McClure & use, and it includes the major cereals and forages. Soderstrom 1972), the basal anthecium staminate Because of the great diversity of Poaceae or neuter (very rarely bisexual) and the apical and its wide variability (Watson & Dallwitz bisexual, with the articulation between rachilla 1992), researchers have traditionally divided it and pedicel below the glumes; and (2) spikelets into subfamilies. This division was initially based exhibiting from one to many anthecia, all bisexual on morphological, anatomical, cytological, and or at least one basal bisexual, and the articulation chromosomic characters, with molecular data being above the glumes, corresponding, respectively, to added more recently. Hence, the number of accepted the series Panicaceae and Poaceae by Bentham & subfamilies and the characters used to determine Hooker (1880). These groups were later accepted them have varied through time. In the seminal as the subfamilies Panicoideae and Festucoideae, publication of GPWG (2001), which proposed a respectively (Hitchcock 1950). Prat (1936) added new subfamilial classification of Poaceae based on the subfamily Bambusoideae, also based on morphological and molecular data, the authors made anatomical and cytological characters, especially a comparison between their classification and the the presence of fusiform cells in the mesophyll. main previous proposals of classification. Later, Pilger (1956) accepted a larger number of The objective of this study is to review subfamilies: Andropogonoideae, Anomochlooideae, different aspects of the taxonomy of Poaceae, Eragrostoideae, Festucoideae, Micrairoideae, including morphology and subfamily classification, Olyroideae, Oryzoideae, and Panicoideae. and to consider the relationship between chorology Parodi (1961) proposed a classification and habitat for different groups. An overview of of the Argentinean grasses in the subfamilies the taxonomic studies of Poaceae in Brazil and of Bambusoideae, Oryzoideae, Phragmitoideae, the possibilities within this field of research is also Festucoideae, Eragrostoideae, and Panicoideae. provided. This classification was used for a long time by 1 Universidade Federal do Rio Grande do Sul, Depto. Botânica, Av. Bento Gonçalves 9500, Prédio 43433, bl. 4, 91501-970, Porto Alegre, RS, Brazil. 2Author for correspondance: [email protected] 90 Longhi-Wagner, H.M. agrostologists of Argentina, Uruguay, and southern independent of Bambusoideae, following Parodi Brazil, where, due to their role in cattle raising (a (1961), Stebbins & Crampton (1961) and Valls very important economic activity in this region), (1980); (ii) the division of part of Bambusoideae the study of grasses has been well developed. into the subfamilies Anomochlooideae, Puelioideae, At the same time, Stebbins & Crampton (1961) and Pharoideae, constituting the group with the proposed to divide the North American grasses into most basal forest grasses; (iii) the acceptance of the six families, similar to those outlined by Parodi subfamily Aristidoideae encompassing the genera (1961), except for Phragmitoideae, which was Aristida L., Sartidia De Winter and Stipagrostis named Arundinoideae. Nees, which had been included in Arundinoideae Valls (1980), in his list of the grass genera of by Clayton & Renvoize (1986). Brazil, accepted the same six families mentioned Later, based on molecular phylogeny, by Stebbins & Crampton (1961), but named Sánchez-Ken et al. (2007) acknowledged the Festucoideae as Pooideae, and Eragrostoideae as inclusion of the tribe Micraireae in the subfamily Chloridoideae, according to the nomenclatural Micrairoideae, which had been included in rules prevailing at that time. Arundinoideae by Clayton & Renvoize (1986) and Later, Clayton & Renvoize (1986) published incertae sedis (at least the genus Micraira F. Muell.) Genera Graminum, also recognizing these in GPWG (2001), increasing to 13 the number of six subfamilies. Pooideae, Chloridoideae, and subfamilies accepted. The genus Isachne Benth. Panicoideae consisted of the study by Valls (ca. three species in Brazil), traditionally included (1980), but with a different circumscription for in the tribe Paniceae, subfamily Panicoideae, Bambusoideae and Arundinoideae. Bambusoideae appeared unexpectedly in the clade Micrairoideae included the tribes Oryzeae and Erharteae (Sánchez-Ken et al. 2007). (Oryzoideae, in Parodi 1961; Stebbins & Crampton Regarding the number of accepted subfamilies 1961; Valls 1980), and Arundinoideae included the of Poaceae, more recent studies, using new DNA tribes Micraireae and Aristideae. Aristideae was sequences and larger samples, identify only 12 accepted in Chloridoideae by Valls (1980). The subfamilies again, maintaining Micrairoideae, sixth subfamily accepted by Clayton & Renvoize but placing the subfamily Centothecoideae (1986) was Centhotecoideae, which Valls (1980) (represented in Brazil only by the forest genus considered as part of the tribe Centhoteceae, Orthoclada P. Beauv.) back in the traditional subfamily Arundinoideae. Panicoideae (Sánchez-Ken & Clark 2007, 2010). In addition to their seminal work Genera Among the data used by GPWG (2001), Graminum (Clayton & Renvoize 1986), Clayton et characters are related to fruit and embryo (Reeder al. (2002) were responsible for the development of 1957), leaf anatomy (Ellis 1986), biochemistry of the project GrassBase – The Online World Grass photosynthesis (Brown 1977; Hattersley 1986), Flora (<http://www.kew.org/data/grasses-db/. and structure of reproductive units, both flowers html>), which uses 1,081 descriptors, most of them and spikelets, or equivalent structures (in more morphological, but some also related to geographic basal subfamilies). distribution, for describing all Poaceae species The currently accepted subfamilies of using the Delta System (Dallwitz et al. 1993). In Poaceae follows the classification available in addition to the descriptions, an interactive key is Soreng et al. (2011): provided for species identification. Anomochlooideae: this is the lineage that The classification proposed by Clayton & first diverged among Poaceae. It is based on Renvoize (1986), including subfamilies and tribes, Anomochloa Brong., a monotypic genus, and also was acknowledged by most agrostologists until includes the genus Streptochaeta Schrad., with the emergence of the classification by the Grass ca. three species (Clayton & Renvoize 1986). Phylogeny Work Group (GPWG 2001). This new These two genera exhibit reproductive structures classification proposed twelve subfamilies based that correspond to spikelets, but which are not on six datasets, five of them molecular and one true spikelets and must have appeared before the structural (macro and micro morphology). The divergence of the subfamily Pharoideae (GPWG main changes in relation to the classification of 2001). As synapomorphies of this subfamily, in Clayton & Renvoize (1986) were: (i) acceptance addition to molecular characters, GPWG (2001) of Erhartoideae (Oryzoideae) as a subfamily cited the fruit type caryopsis and the lateral embryo, Rodriguésia 63(1): 089-100. 2012 Poaceae: an overview 91 which is highly specialized. In addition, there Pooideae), which is exclusively C3, and the other is the presence of fusiform and arm-cells in the clade is PACCAD (Panicoideae, Arundinoideae, mesophyll, characters which are present in most Chloridoideae, Centothecoideae, Aristidoideae, members of other forest Poaceae subfamilies. and Danthonioideae). This second clade also has These two genera are exclusively Neotropical and Kranz syndrome in most of its members, and it is occur mainly in the Atlantic Forest. Anomochloa assumed that this syndrome evolved more than marantoidea Brong., known from a few disturbed once in Poaceae (GPWG 2001). More recently, areas in southern Bahia, is included in the list of Sánchez-Ken et al. (2007) denominated the clade endangered species of Brazil published by the PACCAD as PACCMAD, because the subfamily Ministry of the Environment (MMA 2008). The Micrairoideae was included. Clark (2009) named genus Streptochaeta has two species in tropical this clade PACMAD, as recent studies suggested Brazil (Filgueiras & Gonçalves 2006);