Biodiversity Data Journal : Taxonomic paper

Chromosome studies in the aquatic monocots of Myanmar: A brief review with additional records
Corresponding author: Yu Ito (yu.ito@canterbury.ac.nz), Nobuyuki Tanaka (nbtanaka@makino.or.jp)
Academic editor: Lorenzo Peruzzi
Received: 11 Feb 2014  Accepted: 08 May 2014  Published: 13 May 2014
© 2014 Yu Ito, Nobuyuki Tanaka.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0) which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Ito Y, Tanaka N (2014) Chromosome studies in the aquatic monocots of Myanmar: A brief review with additional records. Biodiversity Data Journal 2: e1069. doi: 10.3897/BDJ.2.e1069

Myanmar (Burma) constitutes a significant component of the IndoMyanmar biodiversity hotspot, with elements of the Indian, the Indochina, and the SinoJapanese floristic regions, yet thus far only a few reliable sources of the country's flora have been available. As a part of a contribution for the floristic inventory of Myanmar, since it is important in a floristic survey to obtain as much information as possible, in addition to previous two reports, here we present three more chromosome counts in the aquatic monocots of Myanmar: Limnocharis flava with 2n = 20, Sagittaria trifolia with 2n = 22 (Alismataceae), and Potamogeton distinctus × P. nodosus with 2n = 52 (Potamogetonaceae); the third one is new to science. A brief review of cytological researches in the floristic regions' 45 nonhybrid aquatic monocots plus well investigated two interspecific hybrids that are recorded in Myanmar is given, indicating that the further works with a focus on species in Myanmar that has infraspecific chromosome variation in the floristic regions will address the precise evolutionary history of the aquatic flora of Myanmar.
Aquatic plants, chromosome counts, Limnocharis, Myanmar, Potamogeton, Sagittaria
With its wealth of plant diversity, Myanmar (Burma) constitutes a significant component of the IndoMyanmar biodiversity hotspot with elements of the India, the Indochina, and the SinoJapanese floristic regions (ca, 13,500 vascular plants:
The aim of floristic research is not only to count the total number of species but also to evaluate the native flora’s evolutionary origins by comparing with related floristic regions. From this aspect, it is useful to obtain as much information as possible, e.g., chromosome data (
Aquatic plants, which is polyphyletically evolved in fern and fern allies, basal angiosperms, monocots, and eudicots, is known as having numerous chromosomal variation, thus an excellent model for this aim. Here, in addition to the previous contributions of chromosome counts for new or noteworthy aquatic plants from Myanmar (Najas tenuis:
Plant materials of Limnocharis flava (Alismataceae), Sagittaria trifolia (Alismataceae), Najas tenuis (Hydrocharitaceae), Nechamandra alternifolia (Hydrocharitaceae), and Potamogeton distinctus × P. nodosus (Potamogetonaceae) were collected in the expeditions to Myanmar (Bago Division and Shan State) in 2008. The collections were rigorously identified based on morphological characters using the original protologues as well as a previous taxonomic treatment by
Root tips collected in the field were pretreated with 0.002 M 8hydroxyquinoline at 4 °C in 12 h, and fixed with freshly mixed Carnoy’s fixative (3: 1 ethyl alcohol: acetic acid) for at least 30 min, and then preserved at 4 °C in 12 h. For microscopic observation, root tips were soaked in 1 N HCl for 1 h followed by 10 min at 60 °C. After being immersed in tap water, the materials were stained in a drop of 1.5% orcein acetate solution on a slide glass in 5 min., and then squashed. Then somatic chromosome numbers of the three taxa were obtained by light microscopic examination. For each species, at least two cells were used to confirm the numbers.
Distribution for each species follows
Chromosome researches for aquatic monocots of Myanmar were reviewed with a broad focus on Myanmar and related floristic regions, i.e., the Indian, the Indochina, and the SinoJapanes floristic regions. The focal species include 45 nonhybrid aquatic monocots listed in
Native to Americas; naturalized to tropical Asia.
Bangladesh, Bhutan, China (nationwide), India (nationwide), Indonesia (Borneo, Java, Sulawesi), Japan, Malaysia (Peninsular), Myanmar, Nepal, Pakistan, Philippines, Thailand; Oceania.
India (Central, Southern), Myanmar, Sri Lanka.
Bangladesh, China (Southern), India (Eastern, Northern, Southern), Myanmar, Nepal, Sri Lanka, Thailand, Vietnam; Yemen, and Sudan.
The chromosome counts given for 45 nonhybrid species of aquatic monocots of Myanmar as well as wellinvestigated two Potamogeton hybrids among them were reviewed with a focus on infraspecific chromosome variation (
The chromosome counts given for 45 nonhybrid species of aquatic monocots of Myanmar as well as wellinvestigated two Potamogeton hybrids among them. Those recorded from neighboring regions are also provided. The species that have no chromosome counts anywhere in the world are shown with n/a. For some species, mostly cosmopolitan ones, only a few representative literature references are given for each chromosome number. Note that due to incapability of original references, some rare chromosome counts are not included in this table: 2n = 18, 42, 48 for Acorus calamus; 2n = 18, 22 for Acorus gramineus (Acoraceae), 2n = 28 for Pistia stratiotes var. cuneata Engl.; 2n = 28 for Pistia stratiotes var. spathulata (Michx.) Engl.; 2n = 20, 50, 60, 80 for Lemna aequinoctialis; 2n = 44 for Lemna trisulca; 2n = 30, 50 for Spirodela polyrrhiza (Araceae); n = 14 (2n = 28), 2n = 10, 12 for Alisma plantagoaquatica; 2n = 22 for Caldesia parnassifolia; 2n = 26, 39 for Limnocharis flava; 2n = 22 for Sagittaria trifolia var. longiloba (Turr.) Mak.; 2n = 22 for Sagittaria trifolia var. sinensis Sims; 2n = 22 for Sagittaria trifolia var. edulis (Sieb.) Ohwi (Alismataceae); 2n = 24 for Blyxa aubertii; 2n = 60 for Najas marina; 2n = 12+1B for Najas marina var. intermedia (Gorski) A. Braun; 2n = 22, 52, 72, 88, 132 for Ottelia alismoides; 2n = 16, 22, 28, 33 for Vallisneria spiralis (Hydrocharitaceae); 2n = 64 for Eichhornia crassipes; 2n = 26, n = 40 (2n = 80) for Monochoria vaginalis (Pontederiaceae); 2n = 60 for Typha angustifolia (Typhaceae). Also refer to previous cytological reviews (aquatic plants:
Order  Family  Species  Chromosome number  Floristic region  

Indian  Myanmar  Indochina  SinoJapanese  Others  
Acorales  Acoraceae  Acorus calamus L.  2n = 24  
Acorales  Acoraceae  Acorus calamus L.  2n = 35  
Acorales  Acoraceae  Acorus calamus L.  2n = 36  
Acorales  Acoraceae  Acorus calamus L.  2n = 44  
Acorales  Acoraceae  Acorus calamus L.  2n = 45  
Acorales  Acoraceae  Acorus calamus L.  2n = 66  
Acorales  Acoraceae  Acorus gramineus Sol. ex Aiton  2n = 24  
Acorales  Araceae  Cryptocoryne crispatula Engl.  2n = 36  
Acorales  Araceae  Cryptocoryne crispatula Engl.  2n = 54  
Acorales  Araceae  Cryptocoryne cruddasiana Prain  n/a  
Acorales  Araceae  Pistia stratiotes L.  2n = 28  
Acorales  Araceae  Landoltia punctata (G. Mey.) Les & D.J. Crawford  n/a  
Acorales  Araceae  Lemna aequinoctialis Welw.  2n = 40 


Acorales  Araceae  Lemna trisulca L.  2n = 20  
Acorales  Araceae  Lemna trisulca L.  2n = 40  
Acorales  Araceae  Lemna trisulca L.  2n = 60 


Acorales  Araceae  Lemna trisulca L.  2n = 80  
Acorales  Araceae  Spirodela polyrrhiza (L.) Schleid.  2n = 40  
Acorales  Araceae  Spirodela polyrrhiza (L.) Schleid.  2n = 42  
Acorales  Araceae  Spirodela polyrrhiza (L.) Schleid.  2n = 80  
Acorales  Araceae  Wolffia globosa (Roxb.) Hartog &Plas  n/a  
Alismatales  Alismataceae  Alisma plantagoaquatica L.  2n = 14 


Alismatales  Alismataceae  Caldesia parnassifolia (Bassi ex L.) Parl.  n/a  
Alismatales  Alismataceae  Limnocharis flava (L.) Buchenau  2n = 20  This study  
Alismatales  Alismataceae  Sagittaria trifolia L.  2n = 22  This study 


Alismatales  Hydrocharita 
Blyxa aubertii Rich.  2n = 40  
Alismatales  Hydrocharita 
Blyxa echinosperma (C.B. Clarke) Hook. f.  2n = 42  
Alismatales  Hydrocharita 
Blyxa echinosperma (C.B. Clarke) Hook. f.  2n = 74  
Alismatales  Hydrocharita 
Blyxa japonica (Miq.) Maxim. ex Asch. & Gürke  2n = 42  
Alismatales  Hydrocharita 
Blyxa japonica (Miq.) Maxim. ex Asch. & Gürke  2n = 72  
Alismatales  Hydrocharita 
Egeria densa (Planch.) Casp.  2n = 46  
Alismatales  Hydrocharita 
Egeria densa (Planch.) Casp.  2n = 48  
Alismatales  Hydrocharita 
Elodea nuttallii (Planch.) H. St. John  2n = 48  
Alismatales  Hydrocharita 
Hydrilla verticillata (L. f.) Royle  2n = 16  
Alismatales  Hydrocharita 
Hydrilla verticillata (L. f.) Royle  2n = 24  
Alismatales  Hydrocharita 
Hydrilla verticillata (L. f.) Royle  2n = 32  
Alismatales  Hydrocharita 
Hydrocharis dubia (Blume) Backer  2n = 16  
Alismatales  Hydrocharita 
Najas graminea Delile  2n = 12  
Alismatales  Hydrocharita 
Najas graminea Delile  2n = 24  
Alismatales  Hydrocharita 
Najas graminea Delile  2n = 36  
Alismatales  Hydrocharita 
Najas indica (Willd.) Cham.  n/a  
Alismatales  Hydrocharita 
Najas marina L.  2n = 12  
Alismatales  Hydrocharita 
Najas marina L.  2n = 24  
Alismatales  Hydrocharita 
Najas tenuis Magnus  2n = 24  
Alismatales  Hydrocharita 
Nechamandra alternifolia (Roxb.) Thwaites  2n = 16  
Alismatales  Hydrocharita 
Ottelia alismoides (L.) Pers.  2n = 44  
Alismatales  Hydrocharita 
Ottelia alismoides (L.) Pers.  2n = 66  
Alismatales  Hydrocharita 
Ottelia alismoides (L.) Pers.  2n = 68  
Alismatales  Hydrocharita 
Ottelia cordata (Wall.) Dandy  n/a  
Alismatales  Hydrocharita 
Vallisneria spiralis L.  2n = 20  
Alismatales  Hydrocharita 
Vallisneria spiralis L.  2n = 24  
Alismatales  Hydrocharita 
Vallisneria spiralis L.  2n = 30  
Alismatales  Hydrocharita 
Vallisneria spiralis L.  2n = 40  
Alismatales  Aponogetona 
Aponogeton lakhonensis A. Camus  n/a  
Alismatales  Potamogetona 
Potamogeton crispus L.  2n = 52  
Alismatales  Potamogetona 
Potamogeton crispus L.  2n = 56  
Alismatales  Potamogetona 
Potamogeton distinctus A. Benn.  2n = 52  
Alismatales  Potamogetona 
Potamogeton distinctus A. Benn. × P. nodosus Poir.  2n = 52  This study  
Alismatales  Potamogetona 
Potamogeton maackianus A Benn.  2n = 52  
Alismatales  Potamogetona 
Potamogeton maackianus A Benn.  2n = 56  
Alismatales  Potamogetona 
Potamogeton × malainoides Miki  2n = 52  
Alismatales  Potamogetona 
Potamogeton lucens L.  2n = 52  
Alismatales  Potamogetona 
Potamogeton nodosus Poir.  2n = 52  
Alismatales  Potamogetona 
Potamogeton octandrus Poir.  2n = 28  
Alismatales  Potamogetona 
Potamogeton wrightii Morong  2n = 52  
Alismatales  Potamogetona 
Stuckenia pectinata (L.) Börner  2n = 78  
Alismatales  Potamogetona 
Stuckenia pectinata (L.) Börner  2n = 84  
Alismatales  Ruppiaceae  Ruppia maritima L.  2n = 20  
Ruppia maritima L.  2n = 40  
Asparagales  Amaryllidaceae  Crinum thaianum J. Schul.  n/a  
Commelinales  Pontederiaceae  Eichhornia crassipes (Mart.) Solms  2n = 32  
Commelinales  Pontederiaceae  Monochoria hastata (L.) Solms  2n = 28  
Commelinales  Pontederiaceae  Monochoria hastata (L.) Solms  2n = 80  
Commelinales  Pontederiaceae  Monochoria vaginalis (Burm.f.) C. Presl ex Kunth  2n = 24 


Commelinales  Pontederiaceae  Monochoria vaginalis (Burm.f.) C. Presl ex Kunth  2n = 48 


Commelinales  Pontederiaceae  Monochoria vaginalis (Burm.f.) C. Presl ex Kunth  2n = 52  
Commelinales  Typhaceae  Typha angustifolia L.  2n = 30  
Poales  Eriocaulaceae  Eriocaulon setaceum L.  n/a 
Of 45 nonhybrid aquatic monocots and two interspecific hybrids among them, more than two thirds have no chromosome variation. Meanwhile, the following nine species have infraspecific chromosome variation, i.e., Acorus calamus, Cryptocoryne crispatula, Blyxa echinosperma, Hydrilla verticillata, Najas graminea, Ottelia alismoides, Vallisneria spiralis, Monochoria hastata, and M. vaginalis (
Potamogeton is known as having numerous interspecific hybrids, and each parental combination is varied from intraploidy crosses to interploidy ones (
Thanks are due to the following personnel in Myanmar for their help in arranging our field work: U. Htun Paw Oo, Exdirector of Nature and Wildlife Conservation Division; U. Soe Win Hlaing, Exdirector General, Forest Department, Ministry of Environmental Conservation and Forestry. We also thank Prof. T. Koyama, director of the Kochi Prefectural Makino Botanical Garden (Japan), who initiated the MyanmarJapanese cooperative program to inventory the plants of Myanmar, and gave us the opportunities to study the Myanmar plants, Prof. J. Murata, curator of the University of Tokyo (Japan), who principally organizes the MyanmarJapanese inventory project, and Dr. T. OhiToma, assistant professor of the University of Tokyo (Japan), who helps the first author to use the facilities of the botanical gardens, the university of Tokyo.
Conceived and designed the study: YI NT. Collected the samples in the field: YI NT. Performed the chromosome observation: YI. Analyzed the data: YI. Wrote the paper: YI. Corrected and revised manuscript: NT.