Flora of the Canadian Arctic Archipelago

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S.G. Aiken, M.J. Dallwitz, L.L. Consaul, C.L. McJannet, R.L. Boles, G.W. Argus, J.M. Gillett, P.J. Scott, R. Elven, M.C. LeBlanc, L.J. Gillespie, A.K. Brysting, H. Solstad, and J.G. Harris

Hippuris ×lanceolata Retz.

English: Six-leaved mare's tail,

French: Queue de cheval.

Hippuridaceae, Mare's tail family.

Published in Observ. Bot. 3: 7. 1783.

Vegetative morphology. Plants 10–50 cm high; perennial herbs; sometimes vegetatively proliferating by fragmentation. Only fibrous roots present. Roots developed from free-floating fragments. Ground level or underground stems horizontal (and semi-horizontal stems, rooting in soft substrates); rhizomatous (but rhizomes are rarely found on herbarium specimens); elongate, or compact. Aerial stems developed; erect; not filiform. Leaves present; heterophyllous, or not heterophyllous (plants growing on damp mud often appear to have only one form of leaf); distributed along the stems; whorled (usually 6 leaves per whorl); dying annually and non-persistent. Petioles absent. Leaf blades simple. Leaf blade bases truncate. Blades (5–)20–80 mm long, 0.6–1.3(–4) mm wide (aquatic leaves; aerial leaves often wider), divaricate, straight, linear (aquatic leaves) or lanceolate or oblanceolate, flat, appearing single-veined or with inconspicuous veins. Blade adaxial surface glabrous. Blade abaxial surface glabrous. Blade margins glabrous; apices acuminate.

Reproductive morphology. Flowering stems circular or oval in cross section. Flowering stems with leaves; rooting at the lower nodes (especially in soft mud). Flowers solitary (in the axil of a leaf). Pedicels absent. Involucral bracts absent. Flowers small; bilaterally symmetrical (zygomorphic) (very reduced); bisexual. Sepals absent (reduced to an inconspicuous 2–4 lobed or sub-entire rim around the top of the ovary). Petals absent. Stamens 1. Anthers purple (turning brown). Ovary inferior; carpels 1; monomerous (pseudo-monomerous). Styles present (elongate slender). Stigmas per ovary 1 (along the whole length of the style). Placentation apical. Ovules per ovary 1. Fruit sessile; dry; an achene; oblong; brown; 1.8–2 mm long; 1–1.2 mm wide; glabrous; surface appearing veinless; not distinctly flattened; indehiscent. Seeds 1.

Chromosome information. 2n = 32.

2n = 32. Zhukova (1982, northeastern Asia); Arohonka (1982, Finland).

Ploidy levels recorded 4x.

North American distribution. Alaska, Yukon (?), Northwest Territories Islands, continental Northwest Territories (?), Nunavut Islands, continental Nunavut, northern Quebec (?), Labrador. Range in the Canadian Arctic Archipelago widespread. Uncommon.

Northern hemisphere distribution. Circumpolar, or circumboreal (probably). Northern Fennoscandian, Kanin–Pechora, Polar Ural – Novaya Zemlya, Yamal–Gydan, Taimyr – Severnaya Zemlya, Kharaulakh, West Chukotka, Wrangel Island, South Chukotka, East Chukotka, West Alaska, Central Canada, Labrador – Hudson Bay.

General notes. In northern Norway, this entity occurs quite independent of its proposed parents, rarely in company with any of them and distinctly outside the range of H. tetraphylla. Elven has seen the same in some western Alaskan sites. It is intermediate between H. tetraphylla and H. vulgaris, but whether it is of hybrid origin has not been fully established (Elven, personal communication, 2002).

In the 1970s the Belgian botanist L. Vanhecke revised much of the northern materials of Hippuris. Two sheets from the Arctic islands in O were redetermined as H. lanceolata, from Southampton Island (Coral Harbour, leg. W.J. Cody, 24/7 1948) and from Baffin Island (Mallik Island, leg. R. Hainault and R. Norman, 10/8 1970). Elven re-examined these specimens and wondered if they were plants of H. vulgaris, possibly in brackish waters. However, when he examined the images of plants photographed at Coral Harbour Southampton Island, 2001, he was convinced that they were H. ×lanceolata. This resulted in Aiken re-examining all collections at CAN from the Canadian Arctic Archipelago and establishing that most of them are H. ×lanceolata, a few are H. vulgaris, and there were none of H. tetraphylla from the islands, although it does occur as far north as Tuktoyaktuk.

Illustrations. • Plants in water: Baffin Island. Plants, lower left with vegetative stems emerging above the water. Growing with Ranunculus pallasii. Nunavut, Baffin Island, Iqaluit, Sylvia Grinnell Park. 1 August, 2005. Aiken 05–077. CAN. • Close-up of Iqaluit plants. Plants, with leaves in whorls of 6 on vegetative stems emerging above the water. Growing with Ranunculus pallasii. Nunavut, Baffin Island, Iqaluit, Sylvia Grinnell Park. 1 August, 2005. Aiken 05–077. CAN. • Habitat: Southampton. Stranded plants growing in a sedge-Dupontia meadow. Nunavut, Southampton Island, Coral Harbour. Aiken and Brysting 01–063. CAN. • Close-up of plants. Stranded plants growing at the edge of a dried-up tundra pool. Aerial stems erect and in flower. Nunavut, Southampton Island, Coral Harbour. Aiken and Brysting 01–065. CAN. • Close-up of plant. Flowering and fruiting aerial stem with a whorl of leaves and a single flower in the axil of each leaf. Most ovaries have been fertilised and are developing into fruit. Nunavut, Southampton Island, Coral Harbour. Aiken and Brysting 01–063. CAN. • Close-up of flowering stem. A flowering stem setting seed with white remains of the stigma on top of the reddish ovaries. Nunavut, Southampton Island, Coral Harbour. Aiken and Brysting 01–063. CAN. • Close-up flowering whorl. Whorl of leaves with flowers in the axils of the leaves. The flowers consist of a single stamen with a pinkish filament (far right) and a globose brown anther that opens on the sides to shed yellow pollen (far left). The thin recurved, structures are withered style-stigmas covered with pollen grains that were received earlier. Nunavut, Southampton Island, Coral Harbour. Aiken and Brysting 01–063. CAN. • Close-up of sterile stem. Close-up of leaves in whorls of six. Leaves are comparatively broad and subacute. Norway, Finnmark, Porsanger, Viekker, brackish marsh. 13 July, 1984. Voucher at TROM. Photograph by R. Elven. • Phenotypic plasticity of leaves. Phenotypically plastic leaves indicate water level. The lower stem leaves are long and soft and were formed when the stem was growing underwater. Towards the apex, the leaves are shorter and stiffer where the stem grew above the water level. N.W.T., Banks Island. CAN 331302. • Close-up of underwater leaves. Long narrow underwater leaves wth 6 per node. N.W.T., Banks Island. CAN 331302. • Phenotypic plasticity of leaves. Phenotypically plastic leaves indicate water level. The lower stem leaves are short and stiff and were formed when the stem was growing above water level. The upper leaves are much longer and softer. They have been formed after water levels rose and the stem was underwater. Nunavut, Ellesmere Island, Lake Hazen. CAN 483723. • Arctic Island Distribution.


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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