R
ESEARCH ARTICLE
doi: 10.2306
/scienceasia1513-1874.2015.41.363
ScienceAsia
41 (2015): 363–376
A taxonomic revision of the tribe Oryzeae (Poaceae) in
Thailand
Paweena Traiperm
a,
∗
, Monthon Norsaengsri
b
, Stephan W. Gale
c
a
Department of Plant Science, Faculty of Science, Mahidol University, Rama 6 Road, Rachathewi,
Bangkok 10400 Thailand
b
Maejo University Phrae Campus 17 Moo 3, Maesai, Rongkwang, Phrae, Thailand 54140
c
Kadoorie Farm & Botanic Garden, Lam Kam Road, Tai Po, New Territories, Hong Kong
∗
Corresponding author, e-mail: paweena.tra@mahidol.edu
Received 24 Dec 2014
Accepted 14 Dec 2015
ABSTRACT: The tribe Oryzeae is represented in Thailand by nine species (one with two varieties) in four genera.
Keys to all taxa are provided together with descriptions, illustrations, photos, ecological data and notes, including
IUCN conservation assessments. The single endemic species, Leersia stipitata Bor, is regarded as globally critically
endangered, whereas all other more widely distributed species are not found to be threatened in Thailand. Two names
are typified: Pharus ciliatus Retz. and Oryza meyeriana (Zoll. & Moritzi) Baill. var. granulata (Nees & Arn. ex G. Watt)
Duist.
KEYWORDS: conservation status,
Hygroryza,
Leersia,
Oryza,
Zizania
INTRODUCTION
The tribe Oryzeae Dumort. belongs to the grass fam-
ily (Poaceae) and comprises around seventy species
in eleven genera distributed in tropical and warm
temperate parts of the world
1
. Its most well known
member is
Oryza sativa, a domesticated cereal and
one of the world’s most important staple foods, but
it also includes other economic species, including
Zizania latifolia
(Griseb.) Turcz. ex Stapf, another
popular cereal and vegetable crop
1
,
2
. Most genera
of the tribe grow in aquatic environments, although
a few occur in forests
2
.
Because of its economic importance, the tax-
onomy and morphology of rice and closely related
genera have been studied in several regions, includ-
ing China
3
, Myanmar
4
, Sri Lanka
5
,
6
, India and Pak-
istan
4
, Malaysia, and Australia
7
. In Thailand, the
tribe has been treated in a checklist that enumerated
eleven species (one with two varieties) in four gen-
era (namely, Oryza L., Leersia Sw., Hygroryza Nees
and Zizania L.), but this lacked a key to the species
and taxonomic descriptions, leading to misidentifi-
cation
8
. More recently, a key to the Thai species
using lemma micromorphology was published
9
, but
that study was unable to provide resolution within a
species complex comprising O. officinalis Wall. ex G.
Watt, O. rufipogon Griff., and O. sativa. Moreover,
taxonomic information and descriptions crucial to
an understanding of the tribe in Thailand are miss-
ing. The present study therefore set out to provide
a complete taxonomic account of Thai Oryzeae, in
advance of its treatment in the Flora of Thailand
series.
MATERIALS AND METHODS
We examined specimens pertaining to all taxa of
tribe Oryzeae collected in Thailand and held at
the following herbaria: AAU, BK, BKF, BM, C, K,
K-W, KKU, L, and QBG. In addition, we consulted
the digitised specimens held at LD, LE, LINN, P, S,
SING and U that are available online. In total, 308
specimens were examined. Observations were also
made of fresh materials of nine taxa collected from
several locations in Thailand during the course of
this study. Type specimens were verified directly at
the herbaria visited where possible, or from digital
images available online if necessary, and relevant
literature was consulted. The conservation status
of all taxa in Thailand was assessed against IUCN
criteria B (geographic range) and D (very small or
restricted population)
10
. All herbarium collections
examined were georeferenced, and GPS coordinates
were recorded for all subpopulations visited in the
field.
Extent of occurrence (EOO) and area of
occupancy (AOO) of each species were estimated in
GeoCAT
11
. For AOO, a 2
× 2 km grid cell size was
used. The species’ ecological attributes (including
inferred habitat requirements and reproductive bi-
ology), number and distribution of locations, esti-
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41 (2015)
mated population size, known or inferred threats,
and the degree to which the populations have un-
dergone, or are projected to undergo decline, were
also considered
10
. The assessment conducted in
this manner for the strict endemic
Leersia stipitata
Bor constituted a full global assessment, but for
all other, more widespread taxa, this “preliminary
assessment” was subject to a further round of veri-
fication following the guidelines for the application
of IUCN criteria at the regional level
12
.
TAXONOMIC TREATMENT
Oryzeae
Dumort. Observ. Gramin. Belg. 83: 135. 1824. Zi-
zanieae
Hitchc., Gen. grasses U.S. 18: 1920.
Annual or perennial herbs. Leaf-blades usually
linear to lanceolate; ligule membranous. Inflores-
cence
a panicle with simple raceme-like primary
branches. Spikelets 1 or 3-flowered with 2 lower
sterile lemmas. Glumes absent or reduced to 2 tiny
lobes on the tip of the pedicel. Lemma membranous
to coriaceous, with or without a straight awn. Palea
similar to lemma. Lodicule 2. Stamens 6. Stigmas 2,
plumose. Caryopsis oblong or terete.
About eleven genera distributed in tropical and
warm temperate regions of the world
1
.
Only 4
genera occur in Thailand:
Hygroryza,
Leersia,
Oryza
and Zizania
8
,
9
. See
Table 1
.
Hygroryza
Nees in Edinburgh New Philos. J. 15: 380. 1833;
Bor, Grasses Burma, Ceylon, India & Pakistan 597.
1960; Phan. Mono. Tom. 12: 181. 1980; Fl. Ceylon
8: 257. 1994; Fl. China 22: 186. 2006; Fl. North
America 24: 46. 2007. Type species: H. aristata
(Retz.) Nees ex Wight & Arn. in Edinburgh New
Philos. J. 15: 380. 1833.— Potamochloa Griff. in J.
Asiat. Soc. Bengal 5: 571. 1836, nom. illeg. superfl.
Perennial, aquatic, stoloniferous herbs. Culms
floating with adventitious roots.
Leaf sheaths
inflated, spongy; leaf blades ovate-lanceolate or
Table 1 Key to genera of Oryzeae in Thailand.
1. Leaf blades ovate-lanceolate or
broadly lanceolate
Hygroryza
1. Leaf blades narrow linear, linear, or
lanceolate
2. Spikelets unisexual
Zizania
2. Spikelets bisexual
3. Sterile lemmas present
Oryza
3. Sterile lemmas absent
Leersia
broadly lanceolate. Inflorescence a panicle, enclosed
by uppermost leaf sheath.
Spikelets
1-flowered.
Glumes
absent.
Lemma
membranous, 5-nerved,
keeled, awned.
Palea
smaller and shorter than
lemma, 3-nerved. Caryopsis terete.
Hygroryza
is a monotypic genus represented
only by H. aristata, an aquatic plant with ovate
or lanceolate floating leaf blades and inflated leaf
sheaths. This species occurs in Pakistan, India, Sri
Lanka, Bangladesh, Nepal, Myanmar, South China
and Taiwan, Thailand, Laos, Cambodia and Viet-
nam
13
.
1.
Hygroryza aristata
(Retz.) Nees ex Wight &
Arn. in Edinburgh New Philos. J. 15: 380. 1833;
Hook. f. in Trimen, Handb. Fl. Ceylon 5: 185.
1900; Bor, Grasses Burma, Ceylon, India & Pakistan
597. 1960; Phan. Mono. Tom. 12: 181. 1980; Fl.
Ceylon 8: 257. 1994; Fl. China 22: 186. 2006;
Fl. North America 24: 46. 2007; Pharus aristatus
Retz. Observ. Bot. 5: 23. 1789.
Type: without
locality, s. coll. s.n. (lectotype LD!); Zizania aristata
(Retz.) Kunth, Révis. Gramin. 1: 8. 1829; Leer-
sia aristata
(Retz.) Roxb., Fl. Ind. ed. 2(2): 308.
1832.— Z. retzii Spreng. Syst. Veg. 2: 136. 1825,
nom. illeg. superfl.— Potamochloa retzii Griff. in J.
Asiat. Soc. Bengal 5: 571. 1836, t. 24, nom. illeg.
superfl.
Fig. 1
A,B,
Fig. 2
.
Culms
15–100 cm long, floating in water or
decumbent on mud in the dry season. Leaf sheath
2–6 cm long, glabrous; ligule c. 0.5 mm long,
truncate; leaf blade 2–7
× 1–2.8 cm, adaxial surface
papillate or scabrous, base rounded to cordate, apex
obtuse. Inflorescence triangular in outline, with 4
or 5 major branches, whorled at apex of peduncle,
base enclosed by uppermost leaf sheath. Spikelet
bisexual, 1-flowered. Glume absent. Lemma 10–
18 mm long, boat-shaped, coriaceous, 5-nerved,
hispid-ciliate along nerves, apex tapering to a long,
stout, straight awn. Paleas 6–8 mm long, very simi-
lar to the lemma but thinner and shorter, muticous,
hispid between nerves. Caryopsis narrowly oblong,
obtuse, turgid, cylindric; hilum linear, as long as
grain, rather faint.
Thailand.— NORTHERN: Chiang Mai, Mae
Rim, 18 Oct. 2005, W. La-ongsri & Prasong 354
(QBG); Phayao, 2 Mar. 1958, Th. Sørensen, K. Larsen
& B. Hansen 1827
(BKF, C, K, L); Phitsanulok,
Thung Salaeng Luang, 19 Jul. 1966, K. Larsen,
T. Smitinand & E. Warncke 511
(BKF); CENTRAL:
Bangkok, 7 Dec. 1919, Kerr 3883 (BK, BM, K);
Bangkok Noi, 3 Feb. 1954, T. Smitinand 1541 (BKF);
SOUTH-EASTERN: Rayong, Chak Phong subdistrict,
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