June 14, 2003

Size; Distribution; Importance;
Morphology; Taxonomy

Bio 3400 Home Page

The Polygonaceae includes many herbs, a number of shrubs, and a few trees. It is a medium-sized family, with 30 genera and 750 species, most of which occur in the north temperate region of the world. We have 31 native species in northern Utah, most being species of Eriogonum.

Many species are mentioned as ornamentals in European garden catalogs, but few are cultivated as ornamentals in this part of the world. There would seem to be an opportunity here for someone interested in developing ornamental cultivars from our native species, most of which are well-suited to arid climates, i.e., xerophytic gardening, the latest "thing" in gardening as water shortages threaten to become common (too many people drinking, taking showers, flushing toilets, etc.) There are some species of minor agricultural importance in North America, notably Fagopyrum esculentum, buckwheat, and Rheum rhubarbarum, rhubarb. 

Members of the Polygonaceae may be herbs, shrubs, trees or vines. Their are generally alternate and simple, but their most distinctive feature is the membranous or hyaline sheath uniting the stipules. This sheath, or ochrea, is present in almost all genera, but not in our largest genus, Eriogonum.

The flowers of the Polygonaceae are usually small, radially symmetric, and white, greenish, or yellowish. The perianth is undifferentiated or poorly differentiated, and consists of 3-6 persistent sepals. These often become enlarged in fruit. There are 5-9 stamens which may have basally fused filaments. The pollen grains vary from tri- to multiporate.

There is a single, usually 3(2-4) carpellate pistil with a superior ovary and as many style branches as carpels. The ovary contains a single, basally attached ovule. At maturity it forms a tetrahedral achene or nutlet which often has the perianth parts attached. The embryo may be straight or curved. 

It may have been the shape of the fruit that gave rise to the name "Polygonaceae", (poly meaning 'many' and gonum meaning 'angle'; remember what I said about the arithmetic abilities of botanists).  

Tannins and oxalic acid are common in members of the Polygonaceae, but betalains are NOT present. I was recently told that Rumex does not belong in the Polygonaceae but the Nepenthaceae. I am waiting to for a references to the arguments supporting the change. according to Judd et al., Rumex and Eriogonum may form a basal complex.  If you are in my class, find out the evidence to support this statement and try to determine whether it supports placing both genera in the Nepenthaceae. And let me know what you find out! 

Eriogonum heracleoides.jpg (114968 bytes)
Eriogonum heracleoides

hyalinesheath2.jpg (33468 bytes)
Hyaline leaf sheath or OCHREA
Eriogonum niveum.jpg (29215 bytes)
Eriogonum niveum
hyalinesheaths.jpg (38248 bytes)

Polygonum arenastrum
Arrows to ochreae
rumex.jpg (42473 bytes)

note enlarged sepals surrounding the fruits