Front Range Seed Analysts
1992 Seed Forum Volume 6 Number 1
SEEDS OF THE FRONT RANGE: Rumex and Polygonum written by Jim Bruce
Last time we discussed the Polygonaceae. The Polygonaceae is a family which enjoys sour, acidic soils and hardpan conditions. We find two genera predominating the family as far as seed analysts are concerned. These are the Rumex and the Polygonum genera. The genus Rumex consists of the plants we commonly call docks and sorrels, while the lady's thumb, smartweeds, and black bindweed are associated with the Polyaonum genus.
Docks and sorrels are generally perennial species arising from a large taproot, crowned by a rosette of fleshy to leathery leaves. The flowers and seeds are borne on long clusters at the top of a fruiting stalk emerging from the rosette. Each seed unit is an achene and three brownish, papery bracts surround the one-seeded unit. Polygonums, on the other hand, tend to be more vine-like in their growth habit and the flowers and seeds arise from dense clustered racemes originating in the axils of the leaves.
Just as their overall growth habit differs, so does their appearance in agricultural fields. Plants of both genera follow the love of the acidic soil, but Polygonum species tend to be found in the lower, wet portions of the field. Often, we find these plants near waterways and adjacent to ponds and lakes. The Polygonums can withstand inundation with water for part of the year and are pleased with heavy soils where air is lacking. The Rumex species are more commonly found in the moister dips of upland fields where hardpans beneath the surface retain moisture because permeability is lacking.
The achenes of these genera can be confused when they are immatureand the colors cross genera lines. As they mature, they draw some distinct character differences. Achenes of the Rumex genus are always 3-sided, with the three sides more or less equal, but sometimes slightly flattened. They have a smooth glossy texture. If one dissects the achenes, we find that the endosperm is generally mottled and the embryo placement is always along the middle of one of the sides. The angles of the achenes are acute. The achene coat often is easily milled off during conditioning. Dock seeds found in legume samples, such as red clover, usually does not possess the bract-like hulls. They are torn off during threshing. Found in grass samples, the dock seed unit will often contain the adhereing bracts. Seed units with the attached bracts are easily identified. Identifying characteristics of this type of unit are the toothed margins of the bracts, the veination, and the presence or absence of the swollen, tubercule-like structure attached to the bract. De-hulled achenes often present a formidable obstacle to identification. Subtle differences in the size, color, and presence of a stalk at the base of the achene and the acuteness of the tapering apex.
Achenes of the Polygonum genus are flat and lenticular, or 3-sided with two sides being equal and the third much broader. This makes the achenes asymetrical in cross section. The texture may be smooth and glossy, slightly pitted, or rough and dull. Usually, they have more texturing than in the docks. The angles of the achenes are rounded, not acute. The endosperm is not usually mottled and the embryo always lies in one of the angles. Most achenes have an abrupt, short point or tip at the apex. Achenes may be found with, or without the adhering sepals which make up the hull.When removed in conditioning, the sepals generally are adhering to the base of the achene. Color of the Polygonums range from brown to black. Certain kinds of sedges may resemble those of the smartweeds. If confused, one only has to dissect the seed unit. Smartweeds have a noticeable embryo,while the sedges have a rudimentary embryo which is not visible.
The Polygonaceae is an interesting family and the seeds are commonly found in seed samples. Most of the docks are entered in state noxious seed lists. It is important that the seed analyst becomes familiar with them. This was once a family, which in bygone days, had value as fodder plants, dyes, and medicinal species. This would indicate that this family contains quite a vitality which for some reason has never been properly developed and mad useful, except in the case of buckwheat. Therefore, as analysts, we recognize it as a family of weeds.