Smooth goosefoot (Chenopodium subglabrum) COSEWIC assessment and status report: chapter 3

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Species Information

Chenopodium subglabrum is in the Chenopodiaceae family in the order Caryophyllales within the subclass Caryophyllidae (Flora of North America (FNA) Editorial Committee 1993). The name Chenopodium comes from the Greek chen meaning goose, and podos meaning foot, due to the shape of the leaves of some species. The descriptive epithet subglabrum refers to the nearly smooth leaves.

The Chenopodiaceae is a cosmopolitan family whose members are characteristically found on xeric, halophytic or salty soils. They are widely distributed in the prairies and plains of North America and drier regions of other continents.

Worldwide, there are approximately 102 genera containing 1400 species in the family Chenopodiaceae. A taxonomic treatment of the goosefoot family was recently published in volume 4 of the Flora of North America series (FNA Editorial Committee 2004). They listed 27 genera in the Chenopodiaceae as occurring in North America, 18 of which are native. There are 34 species of Chenopodium in North America, 20 of which are found in Canada. Of those 20 species, eight are introduced and weedy.

The taxonomy of the Chenopodiaceae and the genus Chenopodium is rather complicated. A special problem exists in the narrow-leaved native taxa and in the frequently introduced species. Crawford (1975) presented a key to ten native diploid species of Chenopodium occurring primarily in the western United States and designated these as the narrow-leaved complex; C. subglabrum belongs to this group. These ten taxa differ on morphological, geographical distribution and ecological grounds (Crawford 1975).

Morphological description

Chenopodium subglabrum is a shallow-rooted, erect or semi-erect annual, with many ascending branched stems, 2-8 dm tall, smooth or sparsely mealy. Leaves are alternate, smooth, linear, 1-veined, somewhat fleshy, base wedge-shaped, margins entire, leaf tip pointed, 1-3(-5) cm long and 0.1-0.2(-0.4) cm long with stalks to 1 cm long. Flower clusters are dense, in terminal and axillary panicles, 6-25 × 5-20 cm, widely spaced, maturing at different times. The floral bracts are variable. The flowers are bisexual, greenish to reddish in colour. There are 5 floral segments, fused into a 0.3-0.4 mm tube. The floral lobes are ovate or orbicular-obovate, 1-1.4 mm, tip obtuse or rounded, keeled, sparsely mealy, and largely covering fruit at maturity. There are 5 stamens opposite the floral lobes and 2 stigmas. The light brown to yellow fruits are ovoid, smooth achenes with non-adherent walls. Seeds are lens-shaped, black, smooth and shiny, 1.2-1.6 mm dia., margins obtuse with a narrow rim (Rydberg 1931; Gleason 1952; Hitchcock et al. 1964; Budd 1979; Moss 1983; FNA editorial committee 2004). See Figure 1.

Figure 1. Portion of Chenopodium subglabrum showing general plant habit (illustration by Laurie Consaul, Canadian Museum of Nature).

Plants from Washington that have been considered to be this species are distinct in having smaller, rougher seeds and more congested, mealy inflorescences than are found in typical C. subglabrum. Morphological and chemical data suggests that C. cycloids, C. pallescens and C. subglabrum represent closely related yet distinct species (Crawford 1975).

In the past, experts have classified Chenopodium subglabrum as a distinct species as well as a variety of C. leptophyllum. Crawford (1975) found, in numerical studies based on only one population of C. subglabrum, that the species is distinct from C. leptophyllum. Morphologically, C. subglabrum, is recognizable on the basis of the following features: 1) entire plant glabrous to sparingly mealy, 2) leaves linear, with one main nerve (vein) from the base, 3) inflorescence open, with the flower clusters widely spaced, 4) seeds 1.2-1.6 mm broad, usually horizontally flattened, and the surface extremely smooth, black and shiny, and 5) fruit wall light brown, often tinged yellow, and very readily separable from the seed. Chenopodium subglabrum is easily distinguished from C. leptophyllum by the latter species’ mealy leaves, seeds mostly 1 mm or less in diameter, and fruit wall firmly attached to the seed. The two taxa do share the features of linear, one-veined leaves (Crawford 1975; Nelson 1902). The flavonoid chemistry of C. subglabrum clearly separates it from C. leptophyllum (Crawford 1974; Crawford 1975).

Crawford and Reynolds (1974), in a numerical study, also found that C. subglabrum was not similar to C. leptophyllum and should probably be treated as a separate species rather than as a variety of the latter. Bassett and Crompton (1982) agreed with this result. The seed protein profile of C. subglabrum is readily separable from that of C. leptophyllum. Studies on seed proteins reinforce other data in lending support to the interpretation of C. subglabrum as taxonomically quite distinct from C. leptophyllum (Crawford and Julian 1976). No intergradations were noted between C. subglabrum and other closely related species in the field or when plants were studied under greenhouse conditions (Bassett and Crompton 1982).

Chenopodiumis distinguished from other genera in the Chenopodiaceae by the following characteristics: annular embryo, stems and branches not jointed, leaves not scale-like, flowers perfect, all with perianth, not enclosed in a pair of bracts, fruit enclosed in the calyx, calyx in fruit not transversely winged, sepals 3-5, stamens usually 2-5, fruiting calyx herbaceous (Rydberg 1931).

Genetic description

The species is diploid with 2n=18 chromosomes. Since C. subglabrum is restricted to sand hill complexes with some component of active sand, there is an ecological barrier to gene flow. Unfortunately, the genetic distinctiveness of the different populations has not been studied to date.