Flora of the Canadian Arctic Archipelago
| Flora of the Canadian Arctic Archipelago | |
English: Dandelion.
Asteraceae (Compositae), Daisy family.
Published in Nom. cons., Prim. Fl. Holsat. 56. 1780.
Vegetative morphology. Plants (1–)5–20(–30) cm high; perennial herbs; with milky juice. Taproot present. Caudex present. Aerial stems a small transition zone between taproot and basal leaves. Leaves not heterophyllous (but sometimes very variable on the same plant); mainly basal, or basal in a rosette; patent, or erect; alternate; dying annually and non-persistent. Petioles present, or absent; 0–40(–70) mm long; winged, or not winged; glabrous. Leaf blades simple. Leaf blade bases attenuate. Blades (10–)20–90(–120) mm long, 2.5–30 mm wide, lanceolate or oblanceolate or obovate, flat, veins pinnate or appearing single-veined. Blade adaxial surface glabrous. Blade abaxial surface glabrous. Blades lobed or not lobed. Blade margins entire (or sub-entire; without dentations on the runcinate lobes), glabrous, with 1–11 teeth on each side of the blade, with teeth all around the blade or toward the apex; degree of incision (0–)50–95%; apices acuminate, or acute.
Reproductive morphology. Plants bisexual, or agamospermic (pollen lacking). Flowering stems without leaves. Flowering stems hairy. Flowering stems woolly. Flowering stem hairs simple (and floccose near the capitulum); longer than the diameter of the flowering stem; white or translucent (if applicable). Inflorescences solitary heads. Flowering heads 8–30 mm deep; (5–)7–40 mm wide; with only ligulate florets. Inflorescences not elongating as the fruit matures (it is the beaks of the achenes that become long and slender and carry the pappus higher in the capitulum). Pedicels absent. Involucral bracts present. Number of rows 2–4. Outer involucral bracts mostly green (often with two conspicuous lines); lying adjacent to the flowers, or spreading to erect; lanceolate, or ovate; 2.5–11 mm high; 0.8–4.5 mm wide; glabrous. Inner involucral bracts linear, or lanceolate; 8–20 mm high; 1–3.5 mm wide; margins wide, scarious for at least one quarter of the bract, or narrow and scarious, less than one quarter of the bract; apex prominently horned, or sometimes callused, but without a prominent horn, or with or without horns or calluses, or entire. Flowers per inflorescence 30–60; bilaterally symmetrical (zygomorphic). Sepals represented by a pappus. Pappus with a single row of hairs; yellowish, or whitish. Ligulate florets pappus 4–10 mm long. Petals conventional; fused; 5; white, or yellow, or pink; with contrasting markings, or without contrasting markings. Corolla flat, strap-like. Ray florets limb 0.8–3 mm wide. Ligulate florets limb 25–60 mm long; 7.5–18 mm wide. Stamens present, or absent; 5. Anthers yellow; (1.5–)3–4.2 mm long. Ovary inferior; carpels 2; syncarpous. Styles 1. Stigmas per ovary 2. Placentation basal. Ovules per ovary 1. Fruit sessile; with calyx persisting; dry; cypselas; obovate; yellowish, or black, or brown, or red, or straw-coloured; 2.5–5 mm long; 0.7–1.2 mm wide; glabrous; surface appearing veinless, or venation ribbed; indehiscent. Cypselas beak stout, shorter or similar in length to the body, or slender, often much longer than the body; surface spinulose (at least at the apex); surface in upper half, or throughout. Seeds 1.
Chromosome information. 2n = 16, or 24, or 32, or 40.
Indigenous knowledge. Porsild (1953) stated that the tender, young leaves of all species, especially when blanched, make an excellent salad, and throughout the summer the leaves may be used as a potherb.
Burt (2000) stated that there is no evidence that dandelions were used by Inuit around Bathurst Inlet.
North American distribution. Range in the Canadian Arctic Archipelago widespread. Common.
Economic uses. Medicinal uses. Small and Catling (1999) reported that as a medicinal plant dandelion has been used at least since the time of the Arabian physicians of the 10th and 11th centuries. Root extracts were once used extensively as a diuretic (to promote urination), and are still sometimes so employed. Dandelion has also been said to be useful for treating jaundice and other liver ailments. Both of these medicinal properties seem to trace to the Doctrine of Signatures, whereby aspects of plants are said to signal their medicinal uses. The yellowness of dandelion flowers was interpreted as a sign that jaundice (which causes yellow colouration) and other liver diseases could be treated. The juiciness of the dandelion, suggestive of water retention, was interpreted as indicating usefulness as a diuretic. For most people the only hazard of consuming dandelion is excessive urination. Overuse of diuretics can lower the level of potassium ions and lead to muscular weakness and constipation.
The bitter resin in the roots and shoots contains taraxacin, taraxerin, taraxerol, taraxasterol, inulin, gluten, gum, potash, choline, levulin, and putin. The dried plant contains 2.8% tannins (Williams et al. 1996).
Non-Medicinal uses. Dandelion has been consumed for thousands of years as food. Almost all parts of the dandelion can be eaten. The nutritive value of dandelion greens, particularly for vitamin C, is much higher than that of most other salad plants. Dandelion is grown commercially as a food plant in northern Europe. In Canada, over 50 commercially sold medicinal preparations contain dandelion (Small 1997).
There are indications that seeds of dandelions were deliberately brought to North America by the Mayflower pilgrims, quite possibly to grow as a garden plant. The dandelion has been declared an endangered wildflower in England (Small and Catling 1999).
General notes. The common name "dandelion" comes from the French dente de lion, which refers to the toothed leaves and translates as "tooth of the lion" (Burt 2000).
Many Taraxacum species do not produce fertile pollen, but produce their seed by parthenogensis (without fertilisation). This mechanism, which does not involve genetic exchange of material between two plants, results in minor variations persisting and leads to problems in plant identification. Elven (personal communication, 2005) noted that in northern and central Europe, nearly a thousand such "forms" have been given species names. The value of this naming is disputed, as some groups probably produce new agamospecies more rapidly than botanists can name them. Separable agamospecies have emerged after the introduction of the lawnmower, and there are specialised golf course agamospecies. The arctic dandelions are more conservative, have probably existed for much longer, and have more taxonomic reality.
Along the arctic coast, most dandelions are associated with soil that has been enriched by nesting birds, burrowing mammals, or humans. They are common on bird nesting islands but even there they tend to become establish at the edge of traditional nests, where the incubating bird defecates over the edge of the nest. They also become established below traditional raptor nest sites on cliffs (Burt 2000).
Porsild (1939) reported that the scapes in arctic Taraxacum during their life cycle often perform a series of characteristic movements. In the early stages the heads with their short scapes are hidden among the rosette leaves. Later, when the heads are nearly full grown but still firmly closed, they emerge because of the rapid elongation of the scapes. The upper portion of the scape at first is sharply hooked and the head at this stage is nodding, but when it opens, the scape gradually straightens out. After flowering, the entire scape bends downward so that the head often touches the ground or is hidden among the leaves. When the cypselas are ripe, the scape once more becomes erect and at the same time grows to more than double its former length. These movements are effected by the unequal intercalary growth of the scape, which derives its strength solely from epidermal or sub-epidermal layers of collenchyma. There is no other mechanical tissue except the lignified parts being the walls of the vessels. The rigidity and supporting strength of the scape is thus due to turgor pressure alone. If one attempts to straighten the sharply curved young scape by force, it will bend sharply, but will not reassume its curve. When the mature cypselas have been shed, a process that may take but a few minutes, the scape almost immediately loses it turgor and withers.
Porsild (1939) claimed that most Taraxacum plants in North America have closed heads, a feature that is apparently a further advance in apogamy. In plants where the heads remain closed, the second phase of curving does not occur and only elongation takes place.
Richards and Sell, in Tutin et al. (1976, Flora Europaea 4), accepted 21 sections in Taraxacum for Europe, but only six of these reach the arctic areas, in northern Europe or elsewhere. These six seem to more or less encompass all the reported arctic groups and have been taken up as a framework for the Panarctic Flora checklist (Elven et al. 2003). The sections are based mainly on the works of Hugo Dahlstedt who seems to have been the only scientist working thoroughly with Taraxacum and comparing them in most major areas in the circumpolar zones, in North America (especially Alaska), northern Siberia and Russia, northern Europe, and Greenland. Scientists working in more restricted areas have usually found the need for more sections in their regions (e.g., Richards and Sell in Britain; see Stace (1997), Christiansen (1942) in Iceland, Tzvelev in Russia) but have not checked whether the sections proposed would also function outside their regions. For this reason, the Panarctic Flora checklist (Elven et al. 2003) suggested using Dahlsteds's broad sections.
*Sect. Arctica Dahlst. Acta Fl. Suec. 1: 37. 1929.
Members of the section that occur in the Canadian Arctic Archipelago are as follows:
Taraxacum holmenianum Sahlin aggregate.
Taraxacum hyparcticum Dahlst.
Taraxacum phymatocarpum J.Vahl
Taraxacum scopulorum (A. Gray) P.A. Rydberg (not in this treatment but recently considered to occur on the Canadian Arctic Islands, Brouillet 2006)
Those not in the Canadian Arctic Archipelago are as follows:
Taraxacum sibiricum Dahlst.
Taraxacum alaskanum Rydb. aggregate
Taraxacum arcticum (Trautv.) Dahlst. aggregate
*Sect. Borealia Hand.-Mazz. (sect. Ceratophora (Dahlst.) Dahlst., non Meg.).
Taraxacum ceratophorum (Ledeb.) DC. aggregate that contains the following:
(1) Taraxacum arctogenum ['arctogena'?] Dahlst.
(2) Taraxacum hyperboreum Dahlst. in Ostenf.
*Sect. Spectabilia (Dahlst.) Dahlst. (not in the Canadian Arctic Islands).
Taraxacum croceum Dahlst., in Anderss. and Hesselm. (1900), Bih. Kongl. Svensk. Vetensk.-Akad. Handl. 26, 3, 1: 12. Synonym: T. lapponicum (Kihlm.) Hand.-Mazz.
Porsild (1957) recognised plants with the name T. lapponicum, as well as T. lacerum, as occurring in the Arctic islands. After examining specimens he named at CAN, Brouillet and Aiken (July 2003) concluded that there is one taxon currently under the name T. ceratophorum.
Several other sections have been recognised in Taraxacum, including *Sect. Erythrosperma (H. Lindb.) Dahlst.; also including Sect. Fulva M.P. Christ., based on Icelandic variation, *Sect. Boreigena Dahlst. ex G.E. Haglund, *Sect. Taraxacum (this section included the T. officinale agg.). Elven (personal communication, 2005) noted that more sections are now recognised in the current Panarctic Flora Checklist than was done in Elven et al. (2003), partly owing to recent revisions by British and Nordic botanists.
Of these sections, Arctica and Borealia have their main variation in Northern Asia and the amphi-Beringian (or amphi-Pacific) regions. Sect. Erythrosperma is mainly European and touches on the Arctic in a very few places, one in northern Siberia. The sections Spectabilia and Boreigena have their focus in, respectively, the North Atlantic surroundings and northwestern Europe. Section Taraxacum is very sparingly represented in the Arctic and mainly as more or less casual ruderals. In this section, continuous hybridisation and segregation probably produces new 'biotypes' much more rapidly than it is possible to describe them.
Aiken (June 2001), in a study of Taraxacum specimens from the Canadian Arctic, observed a colour transition between developing cypselas (which are dark red) and more mature cypselas (which are faded to yellowish or straw-coloured) and concluded that cypsela colour is not reliable unless the cypselas are fully developed.
Illustrations. • Plants with small 'burnt-orange' inflorescences. Right, dandelions with burnt-orange coloured heads. Baffin Island, Cape Dorset. 4 August, 2005. Aiken. No voucher. • Close-up of 'unnamed' Taraxacum. Plant beside the marker. This dandelion with smaller more burnt-orange petals than Taraxacum ceratophorum was observed on the beach at Apex, 2002, and at the Eskimo Village site in Sylvia Grinnell Park in 2005. It was the only dandelion observed in Cape Dorset and quite abundant. Nunavut, Baffin Island, Cape Dorset. 2 August, 2005. Aiken. No voucher. • Close-up-of leaves. Plants growing on beach mud. Note patent and deeply runcinate leaves. N.W.T., Tuktoyaktuk. 22 July, 1981. J.M. Gillett 18775. CAN. • Inflorescence setting seeds. Involucral bracts with well-developed horns on the outer and inner involucral bracts. Manitoba, Churchill. Aiken and Brysting 01–009. CAN. • Close-up of cypselas. Cypselas (sometimes incorrectly called achenes) dull brownish, with sculpturing at the apex and long beaks with pappus hairs on top. Manitoba, Churchill. Aiken and Brysting 01–009. CAN.
This publication is available on the internet (posted May 2011) and on CD-ROM (published in 2007). These versions are identical in content, except that the errata page for CD-ROM is accessible on the main index page of the web version.
Recommended citation for the web-based version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. NRC Research Press, National Research Council of Canada, Ottawa. http://nature.ca/aaflora/data, accessed on DATE.
Recommended citation for the CD-ROM version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. [CD-ROM] NRC Research Press, National Research Council of Canada, Ottawa.
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