Polygonaceae; the buckwheat / knotweed / smartweed / dock family

By Patsy Cotterill

My guess is that the buckwheat family (I prefer to call it the dock family) doesn’t score high in popularity stakes. There are a number of reasons for this: the flowers are small and although densely clustered are not particularly showy; several species are inconspicuous weeds of fields and gardens, and a few are plants confined to mountains, often at high altitudes. Included in this last group are androsace buckwheat (Eriogonum androsaceum), the rare, diminutive island koenigia (Koenigia islandica), mountain sorrel (Oxyria digyna) and Lapland sorrel  (Rumex lapponicus) as well as alpine bistort (Bistorta vivipara) which forms a common ground cover in tundra habitats. Species in the wild buckwheat (Eriogonum) genus of the dry southern plains can be eye-catching, particularly the common yellow buckwheat or yellow umbrella-plant (Eriogonum flavum), but these do not make it farther north into the Parkland Natural Region. In late summer car passengers will often spot the dark brown spikes of members of the dock (Rumex) genus rising above the vegetation of fields or ditches, and wonder what they are, but their curiosity usually does not go much farther than that. 

1. Lapland sorrel, Rumex lapponicus, growing on stony tundra on Plateau Mountain, 2021-06-23. Photo: M. Parseyan.

2. Alpine bistort, Bistorta vivipara, in tundra at Cardinal Divide, Whitehorse Wildland Park, 2023-07-15. Photo: P. Cotterill.

3. Yellow umbrella-plant, Eriogonum flavum, in flower at Oldman Gap, south Kananaskis Country, 2021-07-29. Photo: P. Cotterill.

Nevertheless, a number of species have attained fame – or notoriety – in human circles. Garden sorrel (Rumex acetosa), a native of Eurasia, is widely cultivated for food internationally, particularly for use in soups and as a salad green. (It also feeds the larvae of a number of moths and butterflies.) The buckwheats (Fagopyrum species) are perennials, cultivated for their edible seeds which are also used as a flour constituent; they may appear as garden escapes, sometimes growing from bird seed. Rhubarb (Reum rhabarbarum) is popular for both sweet and savoury dishes. Plants known as Persicaria (although recently they have been moved into the genus Bistorta) have become popular as garden ornamentals.(e.g., Persicaria (Bistorta) amplexicaulis).

On the negative side is the infamous, extremely invasive weed, giant knotweed, Reynoutria japonica, known to be capable of invading house basements and reducing property values!

Characteristics of the Polygonaceae

The buckwheat/knotweed/smartweed/dock family, Polygonaceae, contains about 1200 species in 48 genera, which are mostly annual or perennial herbs. The family reaches its greatest diversity in north-temperate regions. Alberta has 11 genera. 

A number of characteristics consistent throughout the family make it distinctive. The family name (based on the genus Polygonum) may come from the fact that a number of species have swollen nodes (points where the leaves join the stem); poly = many; gonum = knee.

The leaves are simple, alternate, often lanceolate, and often well-developed basally. A pair of joined appendages or stipules at the base of the leaf, encircling the stem, is found in many species and is called an ochrea. (Eriogonum is the exception in lacking an ochrea and in having its flowers in flat-topped clusters called umbels.) The flowers are small and regular, although usually clustered into dense inflorescences for show. There are no petals, but the four, five or six sepals are often coloured; after flowering they form an envelope around the fruit. The superior ovary contains only one ovule, which develops into a single fruit, the three-angled or flattened achene. 

In two articles I will briefly profile the species that commonly occur in the Central Parkland Natural Subregion.

The first article will cover the dock genus, Rumex. 

The Docks and Sorrels, Rumex species. 

This genus is distinctive in that its members have a calyx of six sepals, arranged in two rings (whorls) of three, in which the outer ones, called valves, become enlarged, developing “wings” which are deeply veined. These are red, then ultimately brown in colour as the fruits mature. In some species the valves bear central protuberances on the back, called tubercles. Their presence or absence in a species helps in its identification. The valves enclose the three-angled achene. Another significant character in aiding identification of some species is whether or not a tiny knob or joint, visible under x10 magnification, is present on the short, slender flower stalk, which allows it to bend.

Most docks flower in mid-summer and become more eye-catching as the fruits develop in late summer. 

Of the 14 species of Rumex in Alberta, we need consider only about seven that will be encountered in the Parkland.

The sorrels

Four species may be separated off as having unisexual flowers, with the sexes on separate plants. These include the non-native garden sorrel, Rumex acetosa, the mountain sorrel, R. lapponicus, and the very rare mountain species, alpine sheep sorrel, R. paucifolius. Sheep sorrel, R. acetosella,  a non-native, does crop up locally, in disturbed ground or on sand. It is a very slender plant, usually not more than 30 cm tall, with arrow-shaped basal leaves and numerous small reddish or yellowish flowers which appear in early June. An annual or perennial, it can form small patches from creeping roots. 

Sheep sorrel, Rumex acetosella, in bud (sex not determined), on sandy soil in Elk Island National Park, 2013-05-28. Photo: P. Kyle.

The docks

The remaining species all have perfect flowers, that is, both male and female parts are present within the flower, and are perennials.

Wild begonia or veined dock, Rumex venosus, stands out as being a rhizomatous species with very large valves, 1-3 cm across, which are deeply veined and red. Unfortunately, this strikingly attractive plant is confined to sandy soils in the southern part of the Province, and does not enter the Parkland region.

Four further species can be discounted as rare introductions, probably as a result of agriculture. 

Another four species can be considered as the tall, erect, unbranched docks, whose long flower spikes turn from green to red to brown with age.  

Western dock, Rumex occidentalis, is an erect native that can grow to 150 cm tall in moist, natural habitats such as marshes. The basal and lower leaves are largest, reaching 20 cm long. They are oblong-lanceolate with a narrow tip and a rounded base. The inflorescence consists of erect branches of densely packed flowers arranged in small rings (whorls). Western dock can be distinguished from other docks in that the flower valves have entire (not toothed) edges and do not bear any tubercles. They are 2-4 mm long, triangular in shape, and conspicuously veined. The slender, short flower stalks lack any knob-like joints close to the flower. 

1. Western dock, Rumex occidentalis, in flower in marshy area, Bunchberry Meadows, 2023-07-19. Photo: P. Cotterill.

2. Close-up of flowers of western dock, Rumex occidentalis, showing lack of tubercles and conspicuous joints. Marshy area in Bunchberry Meadows, 2023-07-19. Photo: P. Cotterill.

3. Western dock, Rumex occidentalis, in fruit, in oxbow, Whitemud Creek South, 2009-08-26. Photo: P. Cotterill.

Water dock, Rumex britannica, is a similar species, also native, but is much less common, being recorded from a few situations in the area between the North Saskatchewan and Athabasca Rivers. (I have a specimen from North Cooking Lake-Blackfoot Provincial Recreation Area.) The valves are larger at 4-8 mm long, and are ovate to rounded and also lack teeth.  More distinctively, each of the three valves bears a conspicuous tubercle. Like western dock, the flower stalks of water dock do not have obvious joints. 

Field dock, Rumex pseudonatronatus, is a non-native species that may be becoming increasingly common in disturbed, moist sites. Similar to western dock, the valves lack tubercles, but unlike the previous two species the slender flower stalks bear joints. The narrowly lanceolate leaves have a wedge-shaped base and somewhat curly-wavy margins (known as crisped in the literature).

1. Close-up of fruits of water dock, Rumex britannica, showing valves with tubercles, growing in wetland in Cooking Lake-Blackfoot PRA, 1989-09-10. Photo: P. Cotterill.

2. Field dock, Rumex pseudonatronatus, showing developing fruits and wavy-curly leaves, in moist, disturbed hollow in Nisku Prairie, 2025-07-26. Photo: P. Cotterill.

Curled dock, Rumex crispus, is another introduced species of moist ground. It has markedly curly-wavy leaves and these are rounded or cut-off at the base and extend slightly down the stem. The ovate valves bear three tubercles, as in water dock, but one is usually larger than the others. Joints are present on the flower stalks. 

1. Basal part of curled dock, Rumex crispus, growing at Acheson Field Pond, Parkland County. The curly-wavy leaves are evident. 2023-07-05. Photo: P. Cotterill.

2. Flowering portion of curled dock, Rumex crispus, growing at Acheson Field Pond, Parkland County. Tubercles are visible on the valve. 2023-07-05. Photo: P. Cotterill.

Tierra del Fuego dock (formerly known as golden dock), Rumex fueginus, is easily distinguished from the preceding docks because its valves are toothed or fringed along the edge, giving its flower clusters a distinct, spiky appearance. It is also more branched and bushy-looking. A common, native annual of muddy shores, it does not exceed 60 cm in height. The lower leaves are linear-lanceolate, rounded at the base and somewhat wavy. The inflorescence is a branched, open panicle, with small, narrow leaves subtending the rings of flowers; it becomes golden brown as the fruits mature. Tubercles are present. 

1. Close up of developing fruits of Tierra del Fuego dock, Rumex fueginus, showing toothed valves. A joint on the pedicel is clearly visible in the centre of the photo. Dinosaur Provincial Park, 2011-09-28. Photo: P. Cotterill.

2. Tierra del Fuego dock, Rumex fueginus, in fruit at Hodgson Wetland, Edmonton, 2009-08-02. Photo: P. Cotterill.

Triangular-valve dock, Rumex triangulivalvis, is another common dock of wet places. It has a similar bushy habit to Tierra del Fuego dock, with some stems tending to bend towards the ground. The narrowly lanceolate leaves taper towards both ends, and are sometimes folded, and pale green. The valves are triangular-pointed and bear three narrow tubercles.

1. Triangular-valve dock, Rumex triangulivalvis, in flower on moist waste ground, at Rio Terrace, Edmonton. Reddish ochreae are visible where the leaves join the stems. 2010-07-02. Photo: P. Cotterill. 

2. Close-up of developing fruits of triangular-valve dock, Rumex triangulivalvis, in the river valley at Rio Terrace, Edmonton. Tubercles are clearly evident. 2023-07-21. Photo: P. Cotterill. 

Here is a quick key to the common dock species in the Central Parkland region that have perfect flowers.

1. Plants with valves having marginal teeth………………..Rumex fueginus

Plants with valves entire, not having marginal teeth………...2

2. Plants with valves bearing 1-3 well-developed tubercles….3

Plants with tubercles absent or inconspicuous………………..5

3. Flower stalks lacking joints…………………………………Rumex britannica

Flower stalks with joints………………………………………………4

4. Tall, erect plants with leaf margins curly-wavy……Rumex crispus

Lower growing, branched plants with leaf margins flat or slightly wavy

                                                                                  ….Rumex triangulivalvis

5.  Flower stalks without joints…………………………...  Rumex occidentalis

 Flower stalks jointed………………………………………..  Rumex pseudonatronatus

In part two of the series on the Polygonaceae family,  we will look at two other genera in the family that include local species: the smartweeds, Persicaria species, and the knotweeds, Polygonum species.