The Evolution of the Genus Rumex

Topics: Rumex, Sorrel, Curled Dock Pages: 8 (1765 words) Published: March 19, 2013

The Evolution of the Genus Rumex

Allaine M. Garcia
BIO 140 T

October 15, 2012

Taxonomic Description
The genus Rumex commonly known as dock or sorrel has about 200 species of perennial, biennial or annual herbs belonging to the buckwheat family Polygonaceae. It includes hermaphroditic, polygamous, gynodioecious, monoecious, and dioecious species, with the dioecious species being represented by different sex-determining mechanisms and sex-chromosome systems. These herbs have taproots, with usually short caudex, that are sometimes rhizomatous and/or stoloniferous. Its stems may be erect, ascending, prostrate, glabrous or papillose-pubescent. Its leaves may be basal and/or cauline which are alternate and petiolate. The petiolate leaves are ocrea persistent or partially deciduous, and membranous. The petioles are present on basal and proximal cauline leaves, and are absent on distal cauline leaves while bases are not articulated. The leaf blades are variable in shape. Basal (if present) and proximal cauline leaves have blades ranging from broadly ovate or almost orbiculate to linear, becoming progressively smaller and narrower distally. The leaf margins may be entire, basally lobate, flat, occasionally undulate or crisped. The species of this genus may have terminal, sometimes terminal and axillary, panicle-like, and rarely simple inflorescences. Pedicels are present. The flowers may be bisexual or unisexual. There may be 1 or 4-30 flower(s) present per ocreate fascicle, which has stipe-like base. The perianth may appear in green, pinkish, or red color, and are campanulate or glabrous. There may be 5-6 tepals that are proximally connate, sepaloid, or dimorphic. The outer 3 remains small while the inner 3 are usually enlarged. Sometimes 1-3 tepals have their central vein transformed into tuberculate callosity (tubercle). There are 6 stamens. The filaments are distinct, free, and glabrous. The anthers appear in a yellow to brownish yellow color and are shaped in ovate to elongate. There are 3 distinct styles that may be spreading or reflexed. There are also 3 stigmas that are fimbriate or plumose. The achenes are included in accrescent and usually veiny perianth, with color ranging from tan to dark brown, which may be unwinged or weakly winged. Polyploidy is widespread in this genus and the basic chromosome number implies an evolutionary process of chromosome reduction from x=10 toward x=7 through intermediate stages x=8 and x=9.

Fossil Records or Evidences
Rumex has been identified in 59 samples in cold stages of the Cromerian complex or the early Middle Pleistocene in low numbers. The most common species identified is R. acetosella, which is found in 25 samples in an aggregate of 32 samples. R. acetosa has been recorded in 8 Devensian samples, sometimes in large quantities while the species R. angiocarpus, R. tenuifolius, R. conglomeratus, R. maritimus, and R. palustris each appeared in a few samples.

Other evidences include pollen of Rumex found in 90 samples dating back to the Early Pleistocene cold stages. They are present usually in low frequencies. Pollen of R. acetosella has been recorded in 37 Devensian samples while R. acetosa is found in 37 samples that are mainly Devensian but also Early Pleistocene. Pollen of R. crispus has also been recorded.

Distribution Patterns
Rumex species mainly occupy temperate areas especially the northern hemisphere such as Europe, specifically the Alpine countries: Switzerland, Italy, France and Germany; and the United States, but several species have been introduced elsewhere. Some species have been found in the tropics such as Columbia, Brazil, Panama, Guatemala, Hawaii, and Honduras. The following is a table containing a list of some species representing the four subgenera of the genus Rumex and their respective place of collection and an image of collection sites for Rumex. Table 1. Some species of the genus Rumex and their area of precedence.  |  |...

References: Charlesworth, D. 2002. Plant sex determination and sex chromosomes. UK: Nature Publishing Group.
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Godwin, S. H. 1975. The History of British Flora. 2nd ed. UK: Cambridge University Press.
Juarez, C. and J. Banks. 1998. Sex Determination in Plants. Indiana: Current Biology.
McCann, T. 2008. The Geology of Central Europe: Mesozoic and Cenozoic. London: Geological Society.
Mosyakin, S. L. 1754. Rumex Linnaeus. Flora of North America.
Perez, R. N., et al. 2005. The Evolution of Reproductive Systems and Sex-Determining Mechanisms Within Rumex (Polygonaceae) Inferred from Nuclear and Chloroplastidial Sequence Data. Spain.
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West, R.G. 2002. Plant life of the Quaternary cold stages: evidence from the British Isles. UK: Cambridge University Press.
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