Rodriguésia 66(2): 645-657. 2015
http://rodriguesia.jbrj.gov.br
DOI: 10.1590/2175-7860201566227
Micromorphology of the upper anthecium in Mesosetum Steud.
and related genera (Poaceae, Arthropogoninae) and its taxonomic
applications
Anádria Stéphanie da Silva1,3, André Rodolfo de Oliveira Ribeiro1, Mayco Werllen dos Santos Sousa1,
Christopher William Fagg1, Rosana Falcão2 & Regina Célia de Oliveira1
Abstract
Mesosetum is a Neotropical genus with 25 species, and 21 of them occur in Brazil. Mesosetum forms a clade
closely related with Keratochlaena rigidifolia and Tatianyx arnacites. The objective of this work was to establish the taxonomic value of the upper anthecium micromorphology for the group. A total of 96 specimens,
representing all Mesosetum species (except M. wrightii), K. rigidifolia and T. arnacites were examined under a
scanning electron microscope (SEM). PCA and UPGMA analysis were applied using the micromorphological
characters. Fifithteen useful taxonomic characters were identified. We highlight the following characters to
distinguish the Mesosetum species: the presence, type and distribution of papillae on the abaxial surface of the
upper lemma; the presence of unicellular macrohairs and bicellular microhairs; presence or absence of silica
cells and the structure of the germination lid. The present work shows that the micromorphological characters
identified are important taxonomically at the specific level, allowing the species identification in many cases.
Key words: Grass, Keratochlaena, Tatianyx, PCA, UPGMA.
Introduction
Mesosetum Steud. belongs to the subfamily
Panicoideae, tribe Paspaleae. It is inserted in the
subtribe Arthropogoninae, along with 15 other
American genera (Morrone et al. 2012). Within
Arthropogoninae, Mesosetum forms a clade with
Tatianyx Zuloaga & Soderstr. and Keratochlaena
Morrone genera, as observed in many phylogenies
(Giussani et al. 2001; Aliscioni et al. 2003; GPWG
2011; Morrone et al. 2012).
Swallen (1937) proposed 33 binomials
for Mesosetum, but only 25 were recognized as
valid taxa by Filgueiras (1989). The genus has a
predominantly Neotropical distribution, and Brazil
is the centre of diversity with 21 species, being 12
endemic to the country (Filgueiras et al. 2014).
Most of these species occur in Central Brazil, where
a total of 16 species occur, being seven endemic to
this region (Filgueiras et al. 2014).
Mesosetum is characterized by raceme-like
solitary terminal inflorescence, spikelets with the
first glume adaxial to rachis, glume and lower
lemma with tuffs of hairs and caryopsis with linear
hilum (Filgueiras 1986, 1989). All these characters
are homoplastic because they occur in other genera
of the tribe.
There is controversy in the infrageneric
classification of the genus Mesosetum. Chase
(1911) was the first to establish a morphological
delimitation of the genus and proposed two
sections: Mesosetum sect. Mesosetum and M. sect.
Bifaria (Hack.) Chase. Swallen (1937) revised the
genus and recognized 33 species and added four
new sections to those proposed by Chase (1911):
M. sect. Annua Swallen, M. sect. Penicillata
Swallen, M. sect. Loliiformia Swallen, M. sect.
Schlerochloae Swallen and M. sect. Fulva Swallen
(latter equivalent to M. sect. Mesosetum). Pilger
(1940) partially accepted the work of Swallen,
recognizing 30 species and only three sections:
M. sect. Bifaria, M. sect. Eumesosetum Pilg.
and M. sect. Schlerochloae. Filgueiras (1986,
Universidade de Brasília, Inst. Ciências Biológicas, Programa de Pós-Graduação em Botânica, C.P. 04457, 70910-970, Brasília, DF, Brasil.
Embrapa Recursos Genéticos e Biotecnologia, Parque Estação Biológica, Av. W5 Norte (final), C.P. 02372, 70770-900 Brasília, DF, Brasil.
3
Author for correspondence: anadriastephanies@hotmail.com
1
2
Silva, A.S. et al.
646
1989) recognized 25 species distributed in five
sections. This author included M. sect. Annua in
M. sect. Loliiformia, and transferred M. sect. Fulva
(containing the type species of the genus) to M.
sect. Mesosetum.
Investigations on the ornamentation of the
upper anthecium has revealed important taxonomic
information in the Panicoideae (Mejia-Saules &
Bisby 2003; Giraldo-Cañas 2004), specially in the
delimitation of genera and species phylogenetically
related to Mesosetum, e.g. Apochloa Zuloaga
& Morrone, Canastra aristella (Döll) Zuloaga
& Morrone (under Panicum aristellum Döll),
Cyphonanthus Zuloaga & Morrone, Homolepis
Chase, Keratochlaena (under Sclerochlamys,
nom. illeg.), Oncorachis Morrone & Zuloaga,
Stephostachys Zuloaga & Morrone, Streptostachys
Desv., and Tatianyx (Zuloaga & Sordestrom 1985,
Morrone & Zuloaga 1991; Morrone et al. 2007;
Sede et al. 2008, 2009; Zuloaga et al. 2010).
Nevertheless, there are no studies on the upper
anthecium ornamentation using scanning electron
microscopy (SEM) in Mesosetum species.
While Mesosetum is apparently
well circumscribed from the taxonomic and
nomenclatural viewpoint, the identification of
specimens is difficult. The identification keys
and descriptions of many species are based on
a small number of specimens available at the
time of the last two revisions (Swallen 1937;
Filgueiras 1989), which does not represent the
range of the morphological variability of the taxa.
The present work analyses the upper anthecium
micromorphological characters using SEM in
Mesosetum and related species to verify their
taxonomic value, if these characters support the
consistency of the Mesosetum sections proposed
by Filgueiras (1989), and if there are common
character states between the clade MesosetumTatianyx-Keratochlaena.
Materials and Methods
This work is based on the upper anthecium
micromorphology of 24 Mesosetum species,
with a total of 93 specimens analyzed, plus one
of Keratochlaena rigidifolia (Filg., Morrone &
Zuloaga) Morrone & Zuloaga and two of Tatianyx
arnacites (Trin.) Zuloaga & Soderstr. The samples
were obtained from herbarium specimens. The
specimens examined are listed in Table 1 and the
herbaria acronyms are according to Thiers (2014,
continuously updated). The dataset included
all the Mesosetum species except M. wrightii
Hitchc., endemic to Cuba, which had very limited
collections available, and two other related genera:
Tatianyx and Keratochlaena.
The mature anthecia were mounted onto
aluminum metal stubs using carbon double-stick
tape and sputter-coated with platinum without
pretreatment. The material was carried out on
SEM (Jeol JSM 7001S) at 15 KV, at the Electronic
Microscope Laboratories of the University of
Brasilia, and “Embrapa Recursos Genéticos e
Biotecnologia”. Deformed and flaccid immature
anthecia were not considered. The terminology
followed Ellis (1979), Sordestrom & Zuloaga
(1989) and Giraldo-Cañas (2004).
Table 2 shows the descriptors used in the
present work. Significant differences were not
found between the lemma and palea, which
presented similar ornamentation.
Each specimen measured was considered an
operational taxonomic unit (OTU), following (Rohlf
2000). Cluster analysis was carried out to analyze
the taxonomic value of the micromorphological
characters in the genus. The similarity matrix was
based on Jaccard´s coefficient and then unweighted
pair group method with arithmetic averages
(UPGMA) applied in the dendrogram. A cophenetic
matrix was computed from the clustering matrix
in order to assess the correlation between the
matrix of similarity and the dendrogram. Principal
component analysis (PCA) was used based on
the correlation matrix (Tab. 3). All these analyses
were undertaken using the software NTSYS–PC
2.0 (Rohlf 2000).
Results
Micromorphology Characterization
Our results are new to Mesosetum species.
The anthecia can be elliptic, lanceolate or ovate
(M. pappophorum (Nees) Kuhlm.) and the apex
acute to acuminate (M. sect Sclerochloae). The
anthecia vary from glabrous to hairy, with bicellular
microhair and unicellular macrohair short or long.
The surface of anthecia is quite variable, can be
totally smooth (M. pappophorum) to completely
covered by papillae and silica cells. The epidermal
cells vary into shape and size. Stomata (Fig. 1a)
were seen in 16 species, however difficulties in
the technique could hide their presence in the other
species, hence they were not analyzed.
Simple and compound papillae (Fig. 1a,c,e-g)
were found on short and long cells, generally with
Rodriguésia 66(2): 645-657. 2015
Micromorphology of the upper anthecium in Mesosetum
647
Table 1 – Specimens examined for micromorphological characters from upper anthecium. * According to Filgueiras (1989).
Species
Section*
Collection Site
Voucher
Penicillata
s.l. - GO
Glaziou s.n.
Herbarium
K
Bifaria
Água Boa - MT
R.C. Oliveira et al. 2765
UB
Novo Santo Antonio - MT
H. Jancoski et al. 444
UB
Xavantina - MT
H.S. Irwin et al. 16467
UB
Flores de Goiás - GO
A.S. Silva et al. 269
UB
Jerumenha - PI
A.S. Silva et al. 270
UB
Campo Maior - PI
M.S.B. Nascimento 103
K
Bifaria
Poconé - MT
R.C. Oliveira et al. 2766
UB
Loliiformia
Diamantina - MG
T.S. Filgueiras et al. 11321
IBGE
Diamantina - MG
T.S. Filgueiras et al. 1101
IBGE
Cristalina - GO
H.S. Irwin et al. 13337
IBGE
Bifaria
Teresina de Goiás - GO
A.S. Silva et al. 235
UB
Mesosetum blakei Swallen
Penicillata
Zelaya, Nicarágua
W.D. Stevens 8188‒a
K
Mesosetum cayennense Steud.
Mesosetum
Alto Paraíso - GO
R.C. Oliveira et al. 2744
UB
Cachoeira Paraíso - TO
R.C. Oliveira et al. 2848
UB
Mineiros - MT
G.H. Rua 940
UB
La Paz, Bolívia
R. Haase 630
K
La Paz, Bolívia
C.E. White 2318
K
Santa Cruz, Bolívia
B. Bruderreck 70
K
Santa Cruz, Bolívia
J.R.I. Wood et al. 20791
K
Santa Cruz, Bolívia
J.R.I. Wood et al. 20006
K
Santa Cruz, Bolívia
J.R.I. Wood et al. 17248
K
Santa Cruz, Bolívia
J.R.I. Wood et al. 25982
K
Santa Cruz, Bolívia
J.R.I. Wood et al. 13516
K
Mesosetum agropyroides Mez
Mesosetum alatum Filg.
Mesosetum annuum Swallen
Mesosetum ansatum (Trin.) Kuhlm.
Mesosetum arenarium Swallen
Mesosetum bifarium (Hack.) Chase
Mesosetum chaseae Luces
Loliiformia
Bifaria
Mesosetum chlorostachyum (Döll) Loliiformia
Chase
Rodriguésia 66(2): 645-657. 2015
Santa Cruz, Bolívia
J.R.I. Wood et al. 26130
K
Poconé - MT
R.C. Oliveira et al. 2772
UB
Corumbá - MS
A. Allem et al. 1152
CEN
Corumbá - MS
A. Allem et al. 1397
CEN
Corumbá - MS
A. Pott et al 1771
CEN
Furnas - MG
S.C. Pereira et al. 7178
IBGE
Boa Vista - RR
L. Coradin et al. 871
CEN
Boa Vista - RR
L. Coradin et al. 909
CEN
Bolivar, Venezuela
G. Davidse 22876
K
Rio Negro - AM
Spruce 1310
K
Rio Negro - AM
Spruce s.n.
K
Atabapo, Venezuela
G. Davidse 16863
ESA
Silva, A.S. et al.
648
Species
Mesosetum comatum Swallen
Mesosetum compressum Swallen
Section*
Collection Site
Voucher
Loliiformia
Missiones, Argentina
M. Crovetto 8241
Herbarium
BAA
Missiones, Argentina
M. Crovetto 9533
BAA
Missiones, Argentina
M.E. Mulgura 3461
BAA
Pesqueira - PE
D. Andrade-Lima et al. 9438
UB
Bifaria
Brejo da Madre de Deus - PE L.M. Nascimento et al. 393
G.S. Pinheiro et al. 68
IAN
Estreito, Marabá - PA
G.S. Pinheiro et al. 495
IAN
Alto Paraíso - GO
R. C. Oliveira et al. 2722
UB
Alto Paraíso - GO
Teresina de Goiás - GO
H.M. Longhi-Wagner 3934
T. S. Filgueiras et al. 3229
IBGE
SP
Jaguariaíva - PR
J.F.M. Valls et al. 11260
CEN
Jaboticatubas - MG
T. Sendulski 443
CEN
São José do Barreiro - SP
L. Freitas 753
CEN
Estreito, Marabá - PA
Mesosetum elytrochaetum (Hack.)
Swallen
Bifaria
Mesosetum exaratum (Trin.) Chase Penicillata
Mesosetum ferrugineum (Trin.) Chase Mesosetum
Mesosetum filifolium F.T. Hubb.
Penicillata
Mesosetum gibbosum Renvoize Loliiformia
& Filg.
Mesosetum loliiforme (Hochst. ex Loliiformia
Steud.) Chase
Mesosetum longiaristatum Filg.
Bifaria
Mesosetum pappophorum (Nees) Loliiformia
Kuhlm.
Mesosetum penicillatum Mez
Mesosetum pittieri Hitchc.
Penicillata
Sclerochloae
HUEFS
São João del Rei - MG
Glaziou 17385
P
Parauapebas, Pará
C.R. Martins 998
UB
Atabapo, Venezuela
G. Davidse et al. 17209
K
Trinidad, Belize
G. Davidse et al. 32780
K
San Luis, Honduras
R.R. Innes 19
K
Rio de Contas - BA
S. Atkins et al. 14783
ESA
Lençóis - BA
J.R. Pirani et al. 7238
K
Abaíra - BA
R.M. Harley et al. 50772
K
Palmeiras - BA
V.C. Souza et al. 5238
K
Niquelândia - GO
A.S. Silva et al. 247
UB
Brasília - DF
M.W.S. Souza 62
UB
St. Ignatius, Guiana
R. Goodland 226
K
Pakaraima, Guiana
T.W. Henkel 5820
K
Kayserberg, Suriname
K.U. Kramer et al. 3003
K
Teresina de Goiás - GO
R.C. Oliveira et al. 2816
UB
São Domingos - GO
J.F.M. Valls et al. 15812
CEN
São Domingos - GO
J.F.M. Valls et al. 15841
CEN
Flores de Goiás - GO
A.S. Silva et al. 267
UB
Flores de Goiás - GO
J.F.M. Valls et al. 15949
CEN
Flores de Goiás - GO
J.F.M. Valls et al. 15953
CEN
Serra Negra do Norte - RN
M.F. Simon 498
HUEFS
Serra Negra do Norte - RN
C.G.T. Ferreira 254
UFRN
Xavantina - MT
G. Eiten & L.T. Eiten 8541
K
Xavantina - MT
G.D. Smith 81
K
Beni, Bolívia
G. Beck 20682
K
La Paz, Bolívia
Chepo, Panamá
R. Haase 122
H. Pittier 4516
K
K
Rodriguésia 66(2): 645-657. 2015
Micromorphology of the upper anthecium in Mesosetum
Species
649
Section*
Mesosetum rottboellioides (Kunth) Mesosetum
Hitchc.
Herbarium
UB
Cristália - MG
Hatschbach 55064
ICN
Buíque - PE
D.N. Silva et al. 36
UB
M.C. Pesssoa et al. 477
UB
Atures, Venezuela
G. Davidse 15250
K
Atures, Venezuela
G. Davidse 15428
K
Atures, Venezuela
O. Hubber 2335
K
Atures, Venezuela
O. Hubber 5207
K
Atures, Venezuela
O. Hubber 5259
K
Atabapo, Venezuela
J.J. Wurdack 43753
K
Bolivar, Venezuela
J.J. Wurdack 39762
K
Piar, Venezuela
O. Hubber 12154
K
Santa Barbara, Venezuela
M.J. Eden 224
K
Flores de Goiás - GO
A.S. Silva et al. 266
UB
Flores de Goiás - GO
J.F.M. Valls et al. 15937
CEN
Flores de Goiás - GO
J.F.M. Valls et al. 15947
CEN
Flores de Goiás - GO
J.F.M. Valls et al. 15954
CEN
-
Loreto - MA
J.F.M. Valls et al. 8432
CEN
-
Abaíra - BA
W. Ganev 2728
K
Guiratinga - MT
S.S. Silva 133
IBGE
1–3 papillae per cell. In M. loliiforme (Hochst.
ex Steud.) Chase, M. annuum Swallen, M.
arenarium Swallen, M. chlorostachyum (Döll)
Chase, M. chaseae Luces, and M. ansatum
(Trin.) Kuhlm., coalescence between the larger
papillae occurs in the basal and distal portions
of the anthecium, forming cells with two to six
coalescent papillae (Fig. 1e, g).
The silica cells were found in the cross
form (Fig. 1b). They were registered in M.
alatum Filg., M. bifarium (Hack.) Chase,
M. compressum Swallen, M. elytrochaetum
(Hack.) Swallen, M. exaratum (Trin.) Chase,
M. longiaristatum Filg., M. blakei Swallen, and
M. filifolium F.T. Hubb.
The germination lid in the anthecium basal
portion is very conspicuous in all species, and
differences were observed in these structures
(Fig. 1h, i). We identified two new character
states. Unilobed germination lid is present in
Mesosetum alatum (Fig. 1h), M. agropyroides
Rodriguésia 66(2): 645-657. 2015
Voucher
P.A. Reis et al. 331
Serra Branca - PB
Mesosetum sclerochloa (Trin.) Sclerochloae
Hitchc.
Keratochlaena rigidifolia (Filg.,
Morrone & Zuloaga) Morrone &
Zuloaga
Tatianyx arnacites (Trin.) Zuloaga
& Soderstr.
Collection Site
Grão Mogol - MG
Mez, M. chlorostachyum, M. ferrugineum
(Trin.) Chase, M. filifolium, M. gibbosum
Renvoize & Filg., and M. pappophorum. This
is the typical form found in Paniceae (Rost
& Simper 1975; Johnston & Watson 1981;
Giraldo-Cañas 2004), but bilobed germination
lid was observed in the other 17 species (e.g.
M. elytrochaetum, Fig. 1i).
In the third distal portion, the presence
or absence of long macrohairs aided in the
distinction of the Mesosetum species. Only five
species analyzed did not show a conspicuous
hairy anthecium apex. This character contributed
to distinguish M. exaratum from M. filifolium.
Bicellular microhairs were found in M.
cayennense Steud., M. rottboellioides (Kunth)
Hitchc., M. filifolium and M. sect. Bifaria. Only
the panicoid type was registered (Zuloaga &
Soderstrom 1985), with the basal cell smaller
than the lanceolate apical cell with an acute
apex (Fig. 1d, arrow).
Silva, A.S. et al.
650
Table 2 – Micromorphological characters and character states of the upper anthecium of Mesosetum, Keratochlaena,
and Tatianyx species used in the PCA and UPGMA analyses.
1. Papilla on the abaxial surface: absent(0), present(1)
2. Papilla on the germination lid surface: absent(0), present(1)
3. Papilla on the median surface: absent(0), present(1)
4. Papilla on the distal surface: absent(0), present(1)
5. Simple papilla: absent(0), present(1)
6. Compound papilla: absent(0), present(1)
7. Number of papilla per epidermical cell: one per cell(0), more than one per cell(1)
8. Coalescence between the larger papillas: absent(0), present(1)
9. Bicellular microhairs: absent(0), present(1)
10 Unicellular macrohairs: absent(0), present(1)
11. Unicellular macrohairs on the median surface: absent(0), present(1)
12. Unicellular macrohairs on the distal surface: absent(0), present(1)
13. Cruciform silica cells: absent(0), present(1)
14. Germination lid: bilobed(0), unilobed(1)
15. Germination lid lobe width/dorsal spikelet width: narrow(0), equal(1)
Table 3 – Data matrix used in the cluster analysis of Mesosetum and related genera. Character states according
to Table 2
Species/ Character states
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Mesosetum agropyroides Mez
1
0
1
1
1
1
1
0
0
1
0
1
0
1
0
Mesosetum alatum Filg.
1
0
0
1
1
0
0
0
1
1
1
1
1
1
1
Mesosetum annuum Swallen
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
Mesosetum ansatum (Trin.) Kuhlm.
1
0
0
1
1
1
1
1
1
1
0
1
0
0
0
Mesosetum arenarium Swallen
1
1
1
1
1
1
1
1
0
1
0
1
0
0
0
Mesosetum bifarium (Hack.) Chase
1
0
0
1
1
0
1
0
1
1
1
1
1
0
0
Mesosetum blakei Swallen
1
1
1
1
1
0
1
0
0
1
0
1
1
0
1
Mesosetum cayennense Steud.
1
1
1
1
0
1
0
0
1
1
1
1
0
0
0
Mesosetum chaseae Luces
1
0
1
1
1
1
1
1
1
1
0
1
0
0
0
Mesosetum chlorostachyum (Döll) Chase
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
Mesosetum compressum Swallen
Mesosetum elytrochaetum (Hack.)
Swallen
Mesosetum exaratum (Trin.) Chase
1
0
0
0
1
0
0
0
1
1
1
1
1
0
0
1
0
0
1
1
1
1
0
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
Mesosetum ferrugineum (Trin.) Chase
1
1
1
1
0
1
0
0
1
1
1
1
0
1
1
Mesosetum filifolium F.T. Hubb.
0
0
0
0
0
0
0
0
1
0
0
1
1
1
0
Mesosetum gibbosum Renvoize & Filg.
Mesosetum loliiforme (Hochst. ex
Steud.) Chase
Mesosetum longiaristatum Filg.
1
0
1
1
1
1
1
0
0
1
0
1
0
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
1
0
0
1
1
1
1
0
1
1
1
1
1
0
0
Mesosetum pappophorum (Nees) Kuhlm.
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
Mesosetum penicillatum Mez
1
1
1
1
0
1
0
0
0
1
0
1
0
1
0
Mesosetum pittieri Hitchc.
1
1
1
1
1
1
0
0
0
1
0
1
0
1
0
Rodriguésia 66(2): 645-657. 2015
Micromorphology of the upper anthecium in Mesosetum
Species/ Character states
Mesosetum rottboellioides (Kunth)
Hitchc.
Mesosetum sclerochloa (Trin.) Hitchc.
Mesosetum comatum Swallen
Keratochlaena rigidifolia (Filg.,
Morrone & Zuloaga) Morrone & Zuloaga
Tatianyx arnacites (Trin.) Zuloaga &
Soderstr.
Numerical Analysis
651
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
1
1
1
0
1
0
0
1
1
1
1
0
0
0
1
1
1
1
1
1
0
0
0
1
0
1
0
1
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
1
1
1
1
0
1
0
0
0
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1
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0
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0
Figures 2 and 3 show the relationship between
the analyzed species and the micromorphological
characters of the upper anthecium. The UPGMA
dendrogram shows three clearly separated groups
(Fig. 2). A high correlation of 0.91 was found
between cophenetic matrix and similarity matrix.
These major groups have no correspondence
to taxonomic clades, nor genera or sections of
Mesosetum.
The first three axes of PCA (Fig. 3) explained
71.74% of the total variation (50.95% for axis
1, 12.60% for axis 2 and 8.17% for axis 3). The
characters that contributed more to the formation of
the four groups were: presence or absence of papillae,
quantity of papillae per epidermal cell, presence of
hairs on the apex and presence of silica cells.
The absence of papillae was the most important
character to distinguish M. pappophorum, M.
exaratum, and M. filifolium from the other species
(Fig. 2, 3). However, these species did not group.
Group 1 was composed by species of M.
sect. Bifaria (Fig. 2, 3): M. alatum, M. bifarium,
M. compressum, M. elytrochaetum, and M.
longiaristatum. This group shares many characters,
e.g. absence of papillae on the median surface,
unicellular macrohairs on the median and distal
surface, bicellular microhairs and silica cells.
Group 2 is comprised of M. arenarium, M.
annuum, M. chlorostachyum, M. comatum Swallen,
M. loliiforme, M. ansatum, M. chaseae, and Tatianyx
arnacites (Fig. 2, 3). It has more than one papilla per
cell, compound papillae, coalescence between the
larger papillae, and hairy anthecium apex.
Group 3 is characterized by one papilla per
epidermal cell and is composed of M. cayennense, M.
ferrugineum, M. rottboellioides, M. agropyroides, M.
gibbosum, M. penicillatum Mez, M. pittieri Hitchc.,
M. sclerochloa (Trin.) Hitchc., and Keratochlaena
rigidifolia (Fig. 2, 3).
Rodriguésia 66(2): 645-657. 2015
Discussion
Micromorphological characters of the upper
anthecium have recognized taxonomic value and
are widely used in the taxonomy of the Poaceae
(Thompson & Estes 1986; Filgueiras 2001; GiraldoCañas 2001; Oliveira et al. 2008). Our results
reinforce the importance of such characters, but after
analyzing several specimens some of the characters
are more variable than previously expected and should
be used carefully.
Sede et al. (2009) segregated the genera
Oncorachis and Keratochlaena (under Sclerochlamys
nom. illeg.) based on molecular data, and anatomical,
morphological, and micromorphological characters.
In their study, Mesosetum was reported to have a
smooth anthecium, i.e. without papillae and open at
the apex, based on M. cayennense and M. loliiforme.
However, our results differ significantly. We analyzed
populations of each of these Mesosetum species, from
distinct localities (Tab. 1) and the upper anthecia was
closed at the apex and covered by abundant verrucose
papillae (Fig. 1j). Unfortunately, Sede et al. (2009)
did not cite vouchers.
Sede et al. (2009) also reported the apex of
the upper anthecium as glabrous in Keratochlaena
rigidifolia (under Sclerochlamys) supporting the
segregation of this species into a new genus
Keratochlaena. However, we recorded prickly hairs
on the upper anthecium apex in one voucher (Fig. 4a).
On the other hand, a voucher of Tatianyx arnacites
analyzed by Zuloaga & Sorderstrom (1985) had
prickly hairs on the upper anthecium, differing from
the two specimens analyzed in this current study
which had a glabrous upper anthecium apex (Fig. 4d).
Another major divergence was found in our
study with that of Zuloaga & Sorderstrom (1985).
In our study, T. arnacites has simple papillae, and
they are localized in depressions on the epidermis
surface of the anthecium (Fig. 1f). In Zuloaga &
Soderstrom (1985) the papillae are compound and
Silva, A.S. et al.
652
10 µm
a
10 µm
d 10 µm
10 µm
g
10 µm
100 µm
100 µm
b 10 µm
c
e
10 µm
f
h
100 µm
i
j
Figure 1 – a-g. Detail of the upper anthecium in some of the species analyzed. a. Mesosetum cayennense (R. Haase
630) - stomata (arrow). b. M. filifolium (R.R. Innes 19) - silica cells. c. M. pittieri (H. Pittier 4516) - papillae. d. M.
filifolium (C.R. Martins 998) - bicellular microhairs (arrow). e. M. annuum (A.S. Silva et al. 270) - papillae. f. Tatianyx
arnacites (W. Ganev 2728) - papillae. g. M. chaseae (A. Pott et al 1771) - papillae. h. M. alatum (H. Jancoski et al.
444) - unilobed germination lid. i. M. elytrochaetum (R. C. Oliveira et al. 2722) - bilobed germination lid. j. upper
anthecium of M. loliiforme (T.W. Henkel 5820).
not included in depressions. We have observed a
wide morphological variation in Tatianyx and found
distinct micromorphological characters of the upper
anthecium, requiring reevaluation of this species.
In Arthropogoninae, the bicellular microhairs
were observed only in species of Altoparadisium
Filg., Davidse, Zuloaga & Morrone, Canastra
Morrone, Zuloaga, Davidse & Filg. and Homolepis
Rodriguésia 66(2): 645-657. 2015
Micromorphology of the upper anthecium in Mesosetum
653
Figure 2 – UPGMA dendrogram based on Jaccard’s similarity using micromorphological characters of the upper
anthecium for Mesosetum, Tatianyx, and Keratochlaena species. *Bi. Mesosetum sect Bifaria. *Lo. Mesosetum sect
Loliiformia. *Me. Mesosetum sect Mesosetum. *Pe. Mesosetum sect Penicillata. *Sc. Mesosetum sect Sclerochloae.
*The classification of sections follows Filgueiras (1989). . Group 1. . Group 2. . Group 3. . Subgroups
corresponding exactly to sections proposed by Filgueiras (1989).
(Zuloaga & Soderstrom 1985; Filgueiras et al.
2001; Sede et al. 2008). Silica cells in Mesosetum
have the form of crosses, with a minimum of two
grooves (Fig. 1b), differing from those encountered
in other members of Arthropogoninae whose silica
cells has a dumbbell (halteriform) shape (Zuloaga
& Sorderstrom 1985; Filgueiras et al. 2001).
The germination lid is reported as little
evident or conspicuous in Paniceae (Giraldo-Cañas
2004; Filgueiras et al. 2001). In Mesosetum all the
species had a conspicuous germination lid, and we
proposed two new character states for this structure,
i.e. unilobed or bilobed.
According to Zucol (1998, 2000), the form of
silica cells can show a minimum of two grooves,
but it is more like lobes than grooves. They were
mainly found in the distal portion of the abaxial
Rodriguésia 66(2): 645-657. 2015
surface of fertile lemma, like in the majority of
Paniceae (Hsu 1935; Zuloaga & Soderstrom 1985;
Giraldo-Cañas 2004).
The SEM analyses helped to distinguish
between the closely related taxa. Mesosetum annuum
and M. pappophorum, were previously distinguished
by the length of spikelet hairs, according to
Swallen (1937) and Filgueiras (1989). However,
this character is variable between populations,
and sometimes the overlapping of the hair length
brings doubts if the species are indeed distinct. The
micromorphology of the upper anthecium showed
in the present study, supports the separation of these
species with more certainty. Mesosetum annuum has
papillae on all surfaces and a few hairs at the apex
(Fig. 4b), while M. pappophorum shows a totally
smooth and glabrous upper anthecium (Fig. 4e).
654
Silva, A.S. et al.
Figure 3 – PCA using micromorphological characters of the upper anthecium for Mesosetum, Tatianyx, and
Keratochlaena species. . Group 1. . Group 2. . Group 3. . Species not grouped.
The character used by Filgueiras (1989) to
separate M. alatum from M. bifarium (upper glume
with tufts of hairs) is also inconsistent (Ribeiro
2013), when more samples are analyzed. Our results
show that the best character is the germination lid.
Mesosetum alatum is the only species in M. sect.
Bifaria that has a unilobed germination lid and the
width of this structure is equal to the dorsal spikelets,
while in M. bifarium it is narrower. In addition, the
anthecium has one papilla per cell in M. alatum,
while it has at least three or more papillae per cell
in M. bifarium (Tab. 2).
Another case where the morphological
distinction was also supported by unstable characters
is that of M. exaratum and M. filifolium. Swallen
(1937) used the pilosity of the second glume to
support their distinction, while Filgueiras (1989)
put more value on the plant height and leaf blade
length. Mesosetum filifolium shows silica cells and
bicellular microhairs all over the upper anthecium
surface, and a few macrohairs on the distal portion,
while M. exaratum is glabrous and showed one silica
cell in the three examined specimens.
There are two subgroups of species within the
major groups of the dendrogram (Fig. 2, star) that
coincide with the sections suggested by Filgueiras
(1989). The species that compose the section
Mesosetum adopted by this author include M.
cayennense, M. rottboellioides, and M. ferrugineum
and it corresponds to the subgroup identified by
one compound papillae per cell. This section
is characterized by spikelets with ferruginous
indumentum, which is an exclusive character
(Filgueiras 1989). Species of this same group are
associated with Keratochlaena rigidifolia, that is
the sister group of Mesosetum genus. Similarities
in chromosome size and number of species from M.
sect. Mesosetum were also found by Sousa (2014).
Another subgroup found in the dendrogram
using the upper anthecium micromorphological
characters (Fig. 2, star) corresponds to the very
homogenous M. sect. Loliiformia: M. annuum,
M. arenarium, M. chlorostachyum, M. loliiforme
and M. comatum. This section is characterized by
spikelets with an inflated asymmetric lower glume
and the second glume triangular (Filgueiras 1989).
The upper anthecium of this group has more than
one papilla per cell and coalescent papillae.
This study endorses the importance of the
upper anthecium micromorphological characters
for delimitation of Mesosetum species, but the
taxonomic value of these characters are reduced
for higher hierarchical levels. Also a new character
is described, the germination lid bilobed, which
has never before been mentioned. The lack of
Rodriguésia 66(2): 645-657. 2015
Micromorphology of the upper anthecium in Mesosetum
655
50 µm
a
100 µm
b 100 µm
c
100 µm
d
100 µm
e
f
100 µm
Figure 4 – Apex of the upper anthecium in some of the species analyzed. a. Keratochlaena rigidifolia (J.F.M. Valls
et al. 8432). b. Mesosetum annuum (A.S. Silva et al. 270). c. M. pittieri (H. Pittier 4516). d. Tatianyx arnacites (W.
Ganev 2728). e. M. pappophorum (A.S. Silva et al. 267). f. M. cayennense (R. Haase 630).
standard descriptive terms in Poaceae and the lack
of correspondence between vouchers examined and
the description morphological in SEM studies are
still problematic, whereas it brings difficulties to
compare species and their structures. More studies
that include SEM additional character are needed
to achieve a stronger systematic study of this
group, accurate species identification, and more
comprehensive biogeographical relationships.
Acknowledgements
This study was supported in part by Protax
(562340/2010-6), Reflora and CNPq Edital Universal
(474880/2012-5) and Capes for the doctorate grants
Rodriguésia 66(2): 645-657. 2015
to the first two authors. We are grateful to Sueli
Maria Gomes for her assistance with the anatomy
descriptions and help during revision of this paper.
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Artigo recebido em 18/09/2014. Aceito para publicação em 27/03/2015.
Rodriguésia 66(2): 645-657. 2015
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