Printer Friendly

A new record of the invasive species Hydrilla verticillata (Linn.F.) royal on the Iraqi Rivers.


In the last 100 years, increasing world-wide travel and trade has resulted in the introduction of many aquatic plant species to countries beyond their native range, where their subsequent spread has sometimes been extremely rapid [13].

Hydrilla, which is the submerged macrophyte native to Australia, Southeast Asia and Africa [25], However it became a cosmopolitan species that occurs in Europe, Asia, Australia, New Zealand, the Pacific Islands, Africa, Europe, South America, and North America. Although Hydrilla occurs in temperate areas, it tends to be more widespread in tropical areas of the world [18] as well as seen in the marshes of southern Iraq, Hydrilla was identified for the first time in the Iraq in 2006 at two locations: Abo Rizk marsh [3] and Al-Chibaish marshes [1].

H. verticillata is one of the most serious invasive aquatic weed Problems. This plant possesses numerous mechanisms of vegetative reproduction that enable it to spread very rapidly in the environment in which they live, [6] and extensive growths can severely reduce water flow by clogging the filters of irrigation pumps and trash racks, and interfere with boating, water skiing, swimming, fishing and navigation. Dense infestations of Hydrilla can also significantly reduce the holding capacity of storage ponds [27]. According to the Office of Technology Assessment, at least US$ 100 million is spent annually to control aquatic weeds. Additional losses and damages are estimated at around US$ 10 million, giving a total cost of US$ 110 million per year. [22] and [23].

Taxonomy of the Hydrilla:

H. verticillata belong to the family Hydrocharitaceae [15]. It is the only species in the genus Hydrilla but several biotypes occur in its native range. Some biotypes are monoecious (each plant has both male and female flowers) and others are dioecious (each plant bears only male or female flowers). [9] Hydrilla has the general appearance to the untrained observer of being a dicotyledonous plant, but is in fact classified as a monocotyledonous plant. [6]

The latest classification system (known as APG system: Angiosperm Phelogeny Group system), of the families and orders of the flowering plants which based largely on DNA sequences of the chloroplast, nuclear ribosomal, and mitochondrial genes, In this system the order Alismatales put in monocot clad (Fig.1) that included six orders addition to Alismatales, which included (13) family along with Hydrocharitaceae, that the Hydrilla belong to him [5].

Biological and ecological aspects:

Hydrilla is a submersed, herbaceous, perennial aquatic plant. It is capable of living in many different freshwater habitats. It will grow in springs, lakes, marshes, ditches, rivers, or anywhere there is a few inches of water. [7], it has the capacity of high environmental and exceptional ability to adapt in different environmental conditions, for this the Hydrilla can thrives in environmental conditions varying from lentic to lotic, eutrophic to oligotrophic, acid to alkaline, with high to low light availability, and tropical to temperate climate [16] and it is possible to grow up in environments where the salinity (five salinity of sea water) more than 7 ppm [11] it is an important plant that's grows in a variety of aquatic situations: in static water, in water flowing up to 1.8 m/s, and in water from a few centimeters to 15 m deep [27]. So Hydrilla is widely dispersed, colonizing from tropical to temperate regions (up to latitude 53 [degrees] N in Ireland) [8].

This high capacity to spread resulting from low light compensation and saturation points, and a low carbon dioxide compensation point, of Hydrilla, that enabling it to grow in only 1% of full sunlight. [26].


In addition, Hydrilla has developed an inducible C4-acid cycle to combat adverse conditions, such as limiting carbon dioxide, high oxygen concentration, high temperature and irradiance. Therefore, Hydrilla can shift between C3- and C4 -type photosynthesis, depending on the environment. It is believed that the Hydrilla system represents an archetypal form of C4 photosynthesis among angiosperms. [20].

As a result of having a C4-acid cycle, it is able to store carbon dioxide in air spaces and as organic acids derived from the dark phase of photosynthesis. This growth habit enables the plant to compete effectively for sunlight. [21], for example, once the plant reaches the water's surface, it will continue growing horizontally across the water's surface. This growth pattern has the potential to shade other submerged species preventing their growth and establishment and cause imbalances in pH, temperature and dissolved oxygen fluctuations.

With respect to reproduction of the Hydrilla, It has four different forms of reproduction. It can spread by fragments, rhizomes, turions (leaf axis nodes) and seeds [21], but seed production is probably of minor importance to Hydrilla reproduction compared to its successful vegetative reproduction. Although seed production and viability is low compared to many other weeds [17].

The importance of seed production has not been well researched and is not adequately understood. Seeds of many plants can be ingested by birds, carried for long distances, and passed through the gut in a viable condition. If this proves to be true for Hydrilla seed, it may prove to be an important means of natural, long distance dispersal. [18].

Although H. verticillata discovered in south Iraqi marshes, The current study is the first that the H. verticillata observed in the north Iraqi at a little Zab River. So it aims to increase information about this species by study of the shoot morphology, as well as internal structure of stem.

Materials and methods

First sampling:

Specimens of H. verticillata were collected from the Little Zab River, which is flow from the northwestern of Iran and extends for a 402 km inside Iraq. It is one of the important tributaries that entering the Tigris River at northern of Baiji city after passing Altoncoopri.

Second, laboratory work:

Included a morphological and anatomical study, after the collection of samples directly. For the investigation of stem anatomy, short pieces of stem were cut from the internode of a main stem. Thin slices of stem were cut transversely by hand with a razor blade and then stained in a drop of water with toluidine blue [2], then examined by Olympus microscope, and the sections photographed using a digital camera type (Sony, 7.2 MP)

Results and discussion

First morphology aspects:

Hydrilla has external structure makes it confuse with other species that belong to the same family, but there are some morphological aspects which distinguish it from others, which could be clarified as follows:

1--The leaves:

Leave characterized by absent of stomata and bright green color but color may bleached by the sun and become yellowish when the leaves presence out of the water. Hydrilla's leave classified as Linear-elliptic, serrate, acute. they are strap-like with pointed tips (terminating in a single strong spine cell at the apex). leaves were small about 2-4 mm wide and 6-20 mm long, it have saw-toothed leaf margins and visible spines observed at the tip and along the lower midrib. They exhibit a distinct scabrous or harsh marginal and surface texture (Fig. 2B and C). This spines gives the plant a rough texture.

The leaves were attached directly to the stem and whorled around the nodes in groups of 5 leaves, for this character the species under study named as H. verticillatus, which made up of the Greek word "hydro" meaning "water" and the Latin word "verticillus" that means "the whorl of a spindle" Appropriately named, it is an aquatic plant with leaves that are whorled around the stem. [7]. The leaf midvein was single, reddish in color and the reddish color of midvein is one of the most important characteristics of the species under study (Fig. 2 A).

Hydrilla has an axillary leaf scale called a squamula intravaginalis that is found next to the stem at the base of the leaf. This distinguishes it from the other species in the Hydrocharitaceae family.

2--Stems & Roots:

Two types of stems can be distinguish in the species under this study: are under ground stems (Horizontal) and stand stems or Erect (Fig. 3) and the final developed from nods that found along the horizontal stems, and growing as vertical axes that support the branches, leaves and reproductive structures. In the present study length of the stem did not exceed the 30 cm, despite that it is possible grow to several meters [12], stem was a cylindrical shaped and about 0.2 mm, distance between the nodes (internodes) were large (3-5) cm at the base of the stem and become narrow (less than 1 cm) near the apex.

The number of branches varied between (4 and 5) branches. It is worth mentioning that biotype of hydrilla may be know by the growth of stem, in this connection [24] was stated, that the shoot growth of monoecious is generally spread at the sediment surface with numerous root crowns and high shoot densities Once lateral spread slows, shoots grow upward toward the water surface, forming dense canopies. Conversely, dioecious shoots first elongate to the surface and then form profuse and dense branches. According to this information it thinks that the species under study is a monoecious form of Hydrilla because it has branches at the sediment level.

Either horizontal stems or rhizomes, were characterized by the presence of small structures, tend to be white (Whitish), and pea-sized, formed as a distension at the end of those stems, representing tubers which is one of the means of vegetative reproductive structures of Hydrilla. [9], and these structures were observed immersed in the soil between the roots, by this structures can be positively identified Hydrilla form other species that belong to the same family, such as Elodea, which are very similar in appearance with Hydrilla.


Roots observed buried in the hydro-soil, tuber-like and the diameter did not exceed 2 mm. developed at the base of stand stems, (Fig. 3) and characterized by white color and this is consistent with said [18] that the roots of Hydrilla are white and when growing in highly organic soil they may be become brown or reddish color (the color of the sediment) as well as possible it can become a green color when exposed to light as a result of the chlorophyll presence.

Second stem's anatomy:

Transverse sections of H. verticillata stems in the area between the nodes showed three areas: Epidermis, cortex and the cylinder central (Fig. 4A) and that the epidermis cells was not surrounded by clear layer of cuticle and composed of a compact cells containing chlorophyll, either the cortex, it begins with two layers of collenchyma cells, located under the epidermis and is characterized by the absent of air spaces between the cells (Fig. 4 B) and then the earenchyma which is rich in air rooms that appears as lacunae variable in size, however the largest lacunae located in the outer layers of the cortex and then lacunae take's smaller size in the following rows towards the stem's center.

It was noted that these lacunae were arranged in four rows around the central cylinder and usually separated by row of collenchyma cells (that rich by starch grain) between the lacunae adjacent. (Fig. 4 C). The last layer of the cortex, characterized by small-sized and thin walls cells surrounding the central cylinder represents endodermis, that the casparian strip is not clear in it.

With respect to cylinder vascular the xylem tissue were not clear (figure, 4 A and D), but it contained many lacunae beside of endodermis layer, described by [4] as a Metaxylem. The centeral cylinder was occupied by a large size lacunae it was Protoxylem according to previous source, but that the [10] considered it a central intercellular passage, whilst [27] pointed out that stem's section which studied on the area between the node did not show tissue suggests that it xylem. About phloem, the current study showed clusters of blue color cells beside central lacunae, it was believed as sieve tubes and companion cells (Fig. 4 D).




[1.] Al-Kenzawi, M.A.H., 2007. Ecological study of aquatic macrophytes in the central part of the marshes of Southern Iraq. M.Sc. Thesis, Univ. of Baghdad. Iraq. 286 pages.

[2.] Al-Mandeel, F. Abdullah, 2010. Using of Natural products and Biological Features for Potamogeton Species Taxonomy Growing in the Tigris River within Mosul City. Ph.D. thesis, Biology, Unvi. Of Mosul-Iraq. 171pages.

[3.] Alwan, A.R.A., 2006. Past and present status of the aquatic plants of the Marshlands of Iraq. J. Marsh Bull., 1(2): 120-172.

[4.] Ancibor, E., 1979. Systematic Anatomy of Vegetative Organs of the Hydrocharitaceae. Bot. J. Linn. Soc., 78: 237-266.

[5.] APG III, 2009. "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants". Botanical Journal of the Linnean Society, 161: 105-121.

[6.] Arias, R., M.D. Netherland, B. Scheffler, A. Puri and F.E. Dayan, 2005. Molecular evolution of herbicide resistance to phytoene desaturase inhibitors in Hydrilla verticillata and its potential use to generate herbicide-resistant crops. Pest Manag Sci., 61: 258-268.

[7.] Betsy Ewoldt, Lynn Cudlip, Tom Estrem and Heather Cecrle, 2008. Koontz Lake Aquatic Vegetation Management Plan 2008-2012, Marshall and Starke Counties, Indiana. JF New, 51.

[8.] Cook, C.D.K., R. Luond, 1982. A revision of the genus Hydrilla (Hydrocharitaceae). Aquatic Botany, 13: 485-504.

[9.] Gettys, L.A., W.T. Haller and M. Bellaud, 2009. Biology and Control of Aquatic Plants: A Best Management Practices Handbook Aquatic Ecosystem Restoration Foundation (AERF) USA, 200 pages.

[10.] Haberlandt, G., 1914. Physiological Plant Anatomy. McMillian and Co. London, England, pp: 375-377.

[11.] Haller, W.T., D.L. Sutton and W.C. Barlowe, 1974. Effects of salinity on growth of several aquatic macrophytes. Ecology, 55: 891-894.

[12.] Hofstra, D.E. and P.D. Champion, 2006. Organism Consequence Assessment Hydrilla verticillata National Institute of Water & Atmospheric Research (NIWA) Client Report HAM 2006-058f.

[13.] James, C.S., J.W. Eaton, K. Hardwick, 1999. Competition between three submerged macrophytes, Elodea canadensis Michx, Elodea nuttallii (Planch.) St John and Lagarosiphon major (Ridl.) Moss. Hydrobiologia, 415: 35-40.

[14.] JFNew, 2008. Sylvan Lake Aquatic Vegetation Management Plan Update 2008. Noble County, Indiana. Sylvan Lake Improvement Association, 51 pages.

[15.] Jones, R.L., 2000. Plant Life of Kentucky An Illustrated Guide to the Vascular Flora. The University Press of Kentucky, 834 Pages.

[16.] Kahara, S.N., J.E. Vermaat, 2003. The effect of alkalinity on photosynthesis-light curves and inorganic carbon extraction capacity of freshwater macrophytes. Aquatic Botany, 75: 217-227.

[17.] Langeland, K.A. and C.B. Smith, 1984. Hydrilla produces viable seed in North Carolina lakes. Aquatics 6: 20-22.

[18.] Langeland, K.A., 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed". Castanea, 61: 293-304.

[19.] Langeland, K.A., 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed". Castanea, 61: 293304.

[20.] Magnin, N.C., B.A. Cooley, J.B. Reiskind and G. Bowes, 1997. Regulation and localization of key enzymes during the induction of Kranz-less, C4-type photosynthesis in Hydrilla verticillata. Plant Physiol., 115: 1681-1689.

[21.] Monterroso, I., 2005. Comparison of two socio economic assessment methods for the analysis of the invasion process of Hydrilla verticillata in Lake Izabal, Guatemala. M. thesis, Environmental Science, Univ. Autonoma de Barcelona, 133 pages.

[22.] Office of Technology Assessment, 1993. Two case studies: non-indigenous plants in Hawaii and Florida, in Harmful non-indigenous species in the United States, OTA-F565, US Government Printing Office, US Congress, Washington, DC., 233-266.

[23.] Pimentel, D., L. Lach, R. Zuniga and D. Morrison, 2000. Environmental and economic costs of nonindigenous species in the United States. Bioscience, 50: 53-65.

[24.] Poovey, A.G. and K.D. Getsinger, 2010. Comparative Response of Monoecious and Dioecious Hydrilla to Endothall J. Aquat. Plant Manage, 48: 15-20.

[25.] Sousa, W.T., 2011. Hydrilla verticillata (Hydrocharitaceae), a recent invader threatening Brazil's freshwater environments: a review of the extent of the problem. Springer Science, Hydrobiologia, 669: 1-20.

[26.] Van, T.K., W.T. Haller and G. Bowes, 1976. Comparison of the photosynthetic characteristics of three submersed aquatic plants. Plant Physiol., 58: 761-768.

[27.] Yeo, R., R. Falk, J. Thurston, 1984. The Morohology of Hydrilla: Hydrilla verticellata (L.F.) Royle. Aquat. Plant Manage, 22: 1-17.

Dr. Fathi A. Al-Mandeel

Lecturer Environmental and Pollution Control Research Center University of Mosul, Iraq.

Corresponding Author

Dr. Fathi A. Al-Mandeel, Lecturer Environmental and Pollution Control Research Center University of Mosul, Iraq.

COPYRIGHT 2013 American-Eurasian Network for Scientific Information
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Original Article
Author:Al-Mandeel, Fathi A.
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAQ
Date:Feb 1, 2013
Previous Article:Evaluation of physical and physiological profiles of Iranian male elite soccer players.
Next Article:Survey of canopy structure of soybean (Glycine max) and redroot pigweed (amaranthus retroflexus) in competition with each other.

Terms of use | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters