Taxonomy of the genus Oryza (Poaceae): historical perspective and current status

Introduction
T
he genus Oryza L. is classified under the tribe Oryzeae, subfamily Oryzoideae, of the grass family Poaceae
(Gramineae). This genus has two cultivated species (O. sativa L. and O. glaberrima Steud.) and more than 20
wild species distributed throughout the tropics and subtropics. The Asian cultivated rice (O. sativa) is an
economically important crop that is the staple food for more than one-half of the world’s population. All the wild
relative species in the genus Oryza, together with weedy rice and different rice varieties, serve as an extremely
valuable genepool that can be used to broaden the genetic background of cultivated rice in breeding programs
(Brar and Khush 1997, Bellon et al 1998). Fuller exploitation of the wild rice genepool will provide many more
opportunities to significantly enhance rice productivity. More effective conservation management and more efficient
use of the valuable genetic diversity in the rice genepool, however, largely rely on the development of an appropriate
taxonomic and biosystematic framework for the genus Oryza.
Species in Oryza have already attracted enormous attention from scientists worldwide because of their
agronomic importance. Many studies on taxonomy, phylogeny, and genetic relationships of the Oryza species
have been conducted (Roschevicz 1931, Sampath 1962, Tateoka 1963, Sharma and Shastry 1965, 1972, Chang
1985, Vaughan 1989, 1994, Morishima et al 1992, Wang et al 1992, Lu et al 1998). Diversity in Oryza is tremendous,
Dr Baorong Lu, germplasm specialist of IRRI’s Genetic Resources
Center (GRC), collects wild rice Oryza rufipogon in Eastern Nepal.
MINI REVIEWPage 2

5
IRRN 24.3
which is reflected in the different genomes and genomic
combinations in the genus, and in the significant morphological
variation within and between species. On the other hand, the
great morphological variation in this genus also causes certain
taxonomic difficulties, leading to ambiguous delimitation between
some Oryza taxa. In addition, different classification systems or
taxonomic treatments have been proposed by authors who had
access to herbarium specimens representing only certain
geographic regions. This makes the taxonomy of Oryza species
even more complicated. No single system has been generally
accepted by scientists from different parts of the world to date.
Historical perspective and species enumeration
The genus Oryza was first described by Linnaeus (1753), who
recognized only one species, O. sativa, based on the samples of
cultivated rice from Ethiopia. During the past two centuries, more
than 100 species were published in Oryza by different authors
(for review, see Vaughan 1989), which gives this genus great
taxonomic complexity. Baillion (1894) was the first who tried to
make a more systematic classification of the genus. He recognized
five Oryza species and divided them into four sections, i.e., Sect.
Euoryza (O. sativa), Sect. Padia (O. meyeriana), Sect.
Potamophila (O. parviflora), and Sect. Maltebrunia (O.
leersioides and O. prehensilis). The latter two sections have been
treated as independent genera in the current taxonomy of the
tribe Oryzeae (Vaughan 1989). Roschevicz (1931) made a
comprehensive review and detailed studies on Oryza species,
which were considered as the greatest contribution to Oryza
taxonomic research at that time. He established a classification
system with 20 species in four sections, i.e., Sect. Sativa (with 12
species), Sect. Granulata (2 species), Sect. Coarctata (5 species),
and Sect. Rhynchoryza (1 species). This system served as a
foundation for Oryza taxonomic studies thereafter, although
some species have been transferred to other genera of the
Oryzeae. Since then, the genus has been extensively reviewed
and revised by many taxonomists. Table 1 summarizes the number
of species in the major taxonomic treatments of Oryza since its
establishment by Linnaeus in 1753. The number of species varied
from 5 to 27 in different systems established at different times.
The delimitation of the genus Oryza also varied through
time in different systems. The earlier taxonomists, such as Baillion
(1894), Roschevicz (1931), Chevalier (1932), Chatterjee (1948),
Sampath (1962), Tateoka (1963), Sharma and Shastry (1965,
1972), and Oka (1988), offered a wider generic delimitation.
However, I recognize the same generic delimitation of Chang
(1985) and Vaughan (1989), in which the genus Oryza is
characterized by having a spikelet containing a single terminal
fertile floret (composed of a lemma, palea, six stamens, and a
bifid feathery stigma) and two sterile lemmas (sometimes referred
to as glumes) connected to the base of the floret through a rachilla.
O. coarctata is now in Porteresia; O. angustifolia, O. perrieri,
and O. tisseranti are in Leersia, and O. sabulata is in
Rhynchoryza.
The subdivisional treatment
The subdivision of Oryza into four sections by Roschevicz (1931)
had a fundamental influence on subsequent rice taxonomists,
although the sectional epithets have been modified because of
the legitimacy of botanic nomenclature. Sect. Sativa and Sect.
Granulata recognized by Roschevicz (1931) correspond to Sect.
Euoryza and Sect. Padia published by Baillion (1894). According
to the International Code of Botanical Nomenclature (ICBN),
however, the type section should be named Oryza, which should
replace both Sect. Euoryza and Sect. Sativa. Sect. Padia is a valid
epithet because it was legally published by Baillion (1894) earlier
Table 1. Species of Oryza as recognized by different taxonomists. The
“+” indicates species recognized by the author(s). The italic epithets
indicate commonly accepted taxa in modern literature; the bold italic
epithets indicate taxa that are no longer included in the genus Oryza.
Nonitalic epithets indicate names that are not valid anymore in the
genus Oryza.
O. alta
+
+
+
+
+
+
O. australiensis
+
+
+
+
+
+
+
+
+
O. barthii
+
d
+
d
+
d
+
d
+
d
+
+
+
+
O. brachyantha
+
+
+
+
+
+
+
+
O. cubensis
+
O. eichingeri
+
+
+
+
+
+
+
O. glaberrima
+
+
+
+
+
+
+
+
+
+
O. glumaepatula
+
+
i
+
O. grandiglumis
+
+
+
+
+
+
+
+
+
O. granulata
+
b
+
b
+
+
+
h
+
b
+
+
O. latifolia
+
+
+
+
+
+
+
+
+
+
O. longiglumis
+
+
+
+
+
O. longistaminata
+
e
+
e
+
e
+
e
+
+
+
+
O. malampuzhaensis
+
+
+
+
O. meridionalis
+
+
+
O. meyeriana
+
+
+
+
+
+
g
+
+
+
+
O. mezii
+
O. minuta
+
+
+
+
+
+
+
+
+
+
O. nivara
+
+
+
+
O. officinalis
+
+
+
+
+
+
+
+
+
+
O. perennis
+
+
O. punctata
+
c
+
c
+
c
+
+
f
+
c
+
+
+
+
O. rhizomatis
+
O. ridleyi
+
+
+
+
+
+
+
+
+
+
O. rufipogon
+
+
+
+
+
i
+
O. sativa
+
+
+
+
+
+
+
+
+
+
+
+
O. schlechteri
+
+
+
+
+
+
+
+
+
+
O. stapfii
+
+
+
O. angustifolia
+
+
O. coarctata
+
+
+
+
+
+
O. perrieri
+
+
+
+
+
O. subulata
+
+
+
+
+
O. tisseranti
+
+
+
+
+
a
Only includes species currently recognized in Oryza. 
b
O. abromeitiana was recognized. 
c
O.
schweinfurthiana was recognized. 
d
Named as O. breviligulata by the author. 
e
Named as O.
barthii by the author. 
f
O. ubanghensis was recognized. 
g
Including subsp. granulata and subsp.
abromeitiana. 
h
O. indandamanica was recognized. 
i 
Including O. perennis.
Linnaeus (1753)
Baillion (1894)
a
Prodoehl (1922)
Rosche
vicz (1931)
Che
valier (1932)
Chatterjee (1948)
Sampath (1962)
Tateoka (1963)
Ghose et al (1965)
Sharma & Shastr
y (1972)
Chang (1985)
Vaughan (1989)Page 3

6
December 1999
than Sect. Meyeriana named by Roschevicz (1931). Sect.
Coarctatae and Sect. Rhynchoryza should no longer be included
in Oryza, following the present generic delimitation by Chang
(1985) and Vaughan (1989). Table 2 summarizes the subdivisional
treatments of Oryza by different taxonomists at different times.
Among these treatments, the ones by Sharma and Shastry
(1965, 1972) and Vaughan (1989) have been more extensively
accepted in different parts of the world. The subdivisional
treatments by Sharma and Shastry (1965, 1972) seemed to be
influenced by that of Roschevicz (1931), but with a significant
revision in terms of the subdivisional ranks and their species
inclusion. In the systems of Sharma and Shastry (1965, 1972), 26
species were recognized and included in eight (or nine) series of
three sections. Species included in Sect. Oryza and Sect. Padia
by Sharma and Shastry (1965) all conform to the present generic
delimitation of Oryza, but most of the species (including the type
species O. angustifolia) recognized by Sharma and Shastry (1965)
in Sect. Angustifolia have no longer been included in Oryza. Only
O. brachyantha remains in the genus. Therefore, the epithet
Angustifolia should not be valid as a section in Oryza. Considering
that O. brachyantha is morphologically and genetically very
distinct from all other Oryza species, this species should be
treated as a separate section.
Vaughan’s classification of four complexes (1989) was
obviously influenced by that of Tateoka (1962a). Based on an
extensive morphological study of all Oryza species from different
sources, Tateoka (1962a,b, 1963) made a comprehensive revision
of the genus Oryza. He divided the Oryza species into two major
categories, based mainly on morphological variation. The first
group contained morphologically distinct species, such as O.
schlechteri, O. australiensis, O. brachyantha, O. coarctata, O.
angustifolia, O. perrieri, and O. tisseranti, whereas the second
group included species with taxonomic difficulties. He placed all
species belonging to the second group into five complexes, i.e.,
O. latifolia complex (7 species), O. sativa complex (3 species),
O. glaberrima complex (3 species), O. ridleyi complex (2
species), and O. meyeriana complex (2 species). Species between
different complexes had a distinct morphological variation, but
species within complexes had an ambiguous delimitation.
Following this concept, Vaughan (1989) developed a classification
system and recognized 22 species in four complexes (Table 2),
with two species, O. brachyantha and O. schlechteri, outside of
these four complexes. The significant change in this Oryza
classification system is that, based on a thorough study of target
plant materials from all over the world, Vaughan (1989) removed
a few species from Oryza and made the delimitation of this genus
more reasonable. He also provided distribution maps of all Oryza
species and available genomic data for most species, which largely
promoted a better understanding of the species relationships in
the genus. In his later publication titled “The wild relatives of
rice: a genetic resources handbook,” Vaughan (1994) provided
further information for each Oryza species, such as morphological
characterization, distribution, habitat, and species affinities within
the genus. He also included his newly published species, Oryza
rhizomatis Vaughan from Sri Lanka, in this handbook.
A proposed taxonomic treatment
Since the publication of Sharma and Shastry’s taxonomic systems
(1965, 1972), several newly described species, such as O.
meridionalis Ng, O. rhizomatis, and O. neocaledonica Morat,
have been added to Oryza. On the other hand, some species
recognized by Sharma and Shastry (1965, 1972) in their systems,
such as O. cubensis Ekman, O. malampuzhaensis Krish. et
Chand., O. angustifolia Hubb., O. perrieri Camus, and O.
tisseranti A. Chev., have been either considered as invalid epithets
or moved from Oryza to other genera of the Oryzeae. The generic
delimitation of Oryza by Sharma and Shastry (1965, 1972)
therefore needs to be updated to respond to current changes in
the genus. Vaughan’s classification (1989) better reflects the
current circumscription and enumeration of the genus Oryza,
but unfortunately the subdivisional rank “complex” that he
adopted in his system has no legal standing in the International
Code of Botanic Nomenclature (Art. 21.1, Greuter et al 1994). In
addition, this classification system leaves two species outside of
Table 2. Subdivisional treatments of Oryza by different rice taxonomists.
Roschevicz
Chevalier
Ghose et al
Sharma & Shastry
b
Tateoka
c
Oka
Vaughan
c
(1931)
(1932)
(1965)
(1965, 1972)
(1963)
(1988)
(1989)
Sect. Sativa
Sect. Euoryza
Sect. Sativa
Sect. Oryza
O. latifolia
Sect. Oryzae
O. sativa
Sect. Granulata
Sect. Padia
Sect. Officinalis
Ser. Latifoliae
O. sativa
Sect. Schlechterianae
O. officinalis
Sect. Coarctata
a
Sect. Sclerophyllum
a
Sect. Granulata
Ser. Sativae
O. glaberrima
Sect. Granulatae
O. ridleyi
Sect. Rhynchoryza
a
Sect. Rhynchoryza
a
Sect. Padia
O. ridleyi
Sect. Ridleyanae
O. meyeriana
Ser. Schlechterianae
O. meyeriana
Sect. Angustifoliae
a
Others
e
Ser. Meyerianae
Others
d
Sect. Coarctatae
a
Ser. Ridleyanae
Sect. Angustifolia
a
Ser. Brachanthae
Ser. Perrierianae
a
All or some species in this section are no longer included in Oryza. 
b
The treatments by Sharma & Shastry in 1965 and 1972 were essentially the same. In the earlier treatment (1965),
Sect. Oryza included the third Ser. Australienses. 
c
The entity “complex” was used as a subdivisional rank. 
d
Five species were placed outside of any of the complexes. 
e
Two species were
placed outside of any of the complexes.Page 4

7
IRRN 24.3
any of the complexes, which makes the classification incomplete.
I therefore propose a taxonomic system of Oryza basically
following the classification into three sections suggested by
Sharma and Shastry (1965), but with certain modifications to
match current changes in the genus. In my proposed system, 24
species are recognized and placed in three sections, i.e., Sect.
Padia (with 3 series and 6 species), Sect. Oryza (3 series and 17
species), and the newly established Sect. Brachyantha (1 series
and 1 species). This classification mirrors appropriately the
enumeration of Oryza species and their relationships, and it also
gains support through many morphological, cytological, and
molecular studies of the genus.
I. Sect. Padia (Zoll. et Mor.) Baill. (Type: O. granulata Nees et
Arn. ex Watt).
1. Ser. Meyerianae Sharma et Shastry. (Type: O.
granulata).
O. granulata
O. meyeriana (Roll. et Mor. ex Steud.) Baill.
O. neocaledonica Morat
2. Ser. Ridleyanae Sharma et Shastry. (Type: O. ridleyi
Hook. f.).
O. longiglumis Jansen
O. ridleyi
3. Ser. Schlechterianae Sharma et Shastry. (Type:
O. schlechteri Pilger).
O. schlechteri
II. Sect. Brachyantha B.R. Lu, sect. nov. (Type: O. brachyantha
Chev. et Roehr.).
Plantae graciles, annuae; culmi tenues, erecti, glabri; folia
linearia; inflorescentia erecta, racemosa; rami principes
inflorescentiae flexui, nervosi; spicula linearia oblongaque, 8.5-9
× 0.8-1.8 mm; lemmata sterilia glabra, subulata, 1-2 
× 8.5-9 mm,
aliquando absentia; rachila curvata lunae instar; lemma fertilis
mucronatum, 6-8 mm longum, 0.8-1.5 mm latum; aristae robustae,
scabrae, 6-10 cm longae; antherae 1.8-2.5 mm longae.
Plants gracile, annual; culms slender, erect, glabrous; leaves
linear; inflorescence erect, racemose; main axes of inflorescence
flexuous, ribbed; spikelets oblong-linear, 8.5-9 
× 0.8-1.8 mm;
sterile lemmas glabrous, subulate, 1-2 mm long, sometimes
absent; rachilla bent in a comma-shape; fertile lemma mucronate,
6-8 
× 0.8-1.5 mm; awns robust, scabrous, 6-10 cm long; anthers
1.8-2.5 mm long.
4. Ser. Brachyanthae Sharma et Shastry. (Type: O.
brachyantha).
O. brachyantha
III. Sect. Oryza. (Type: O. sativa L.).
5. Ser. Latifoliae Sharma et Shastry. (Type: O. latifolia
Desv.).
O. alta Swallen
O. eichingeri A. Peter
O. grandiglumis (Doell) Prod.
O. latifolia
O. minuta J.S. Presl. et C.B. Presl.
O. officinalis Wall. ex Watt
O. punctata Kotechy ex Steud.
O. rhizomatis Vaughan
6. Ser. Australienses Tateoka ex Sharma et Shastry. (Type:
O. australiensis Domin.).
O. australiensis
7. Ser. Sativae Sharma et Shastry. (Type: O. sativa L.).
O. barthii A. Chev.
O. glaberrima Steud.
O. glumaepatula Steud.
O. longistaminata Chev. et Roehr.
O. meridionalis Ng
O. nivara Sharma et Shastry
O. rufipogon Griff.
O. sativa
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4th International Rice Genetics Symposium set for
October 2000
The Fourth International Rice Genetics Symposium (IRGS) will be
held at IRRI on 22-27 October 2000. The first IRGS was held in
1985. It led to the birth of the Rice Genetics Cooperative (RGC),
which aimed to promote international cooperation in rice genetics.
The same year, the Rockefeller Foundation organized the Interna-
tional Program on Rice Biotechnology, which has played a major
role in advancing the frontiers of rice science, international
collaboration, and human resource development in rice. During
the second IRGS (held in 1990), a unified numbering system for
rice chromosomes and linkage groups was established. More than
500 scientists from 31 countries participated in the third IRGS (held
in 1995). Correct orientation of classical and molecular linkage maps
was one of the symposium highlights.
Major advances in the genetics and molecular biology of
rice have become apparent during the past 15 years. A high-density
molecular genetic map of more than 2,300 DNA markers has been
developed and several genes of economic importance as well as
quantitative trait loci (QTL) have been tagged with molecular
markers. Synteny relationships between genomes of rice and
several other cereals have been established. Molecular marker-
aided selection is being used to move genes from one varietal
background to another and to pyramid genes. Scientists have
developed BAC and YAC libraries and are using them in the physical
mapping of the rice genome. A map-based cloning strategy has
been used to isolate agronomically important genes. Regeneration
from protoplasts of many indica and japonica varieties has allowed
researchers to introduce novel genes into elite germplasm through
transformation. More recently, biolistic and Agrobacterium-medi-
ated transformation procedures have become available.
International programs on rice genome sequencing and functional
genomics have been established. These developments have opened
new frontiers in rice molecular biology, particularly for
understanding the genetic architecture of traits and their
manipulation, modifying gene expression, genome sequencing,
functional genomics, and gene discovery. Researchers are using
these breakthroughs to develop rice varieties with higher yield
potential and yield stability for feeding 50% more rice consumers
by 2025.
The fourth IRGS will feature plenary sessions, oral presen-
tations, and poster sessions. Participants will discuss the latest de-
velopments in rice systematics and evolution, cytogenetics, classical
genetics, tissue and cell culture, molecular markers, genetic engi-
neering, and genomics.