Potamogeton, Linnaeus, 1753

Bobrov, Alexander A., Zalewska-Gałosz, Joanna & Chemeris, Elena V., 2013, Potamogeton × clandestinus (P. crispus × P. natans, Potamogetonaceae), a new natural pondweed hybrid discovered in Europe, Phytotaxa 149 (1), pp. 31-49 : 38-42

Potamogeton × clandestinus A. A. Bobrov, Zalewska-Gałosz, Chemeris, nothosp. nov., Figs. 2–6

(= P. crispus L. × P. natans L.)

Planta hybrida , inter parentes ( Potamogeton crispus et P. natans ) intermedia ; a P. crispo foliis submersis elongatis taeniiformibus, margine integerrimis, planis, foliis natantibus evolutis, stipulis nervis dorsalibus evidentibus binis; a P. natante caulibus compressis, foliis submersis sessilibus, laminosis, stipulis convolutis vel breviter connatis, impersistentibus, ecarinatis, inflorescentiis et pedunculiis brevioribus; a hybrida simili P. ×sparganiifolio et P. ×vepsico partibus omnibus minoribus, caulibus compressis, foliis submersis sessilibus, foliis natantibus raro evolutis, stipulis convolutis vel breviter connatis differt.

Type:— RUSSIA. Vologda reg., Babaevo distr.: Aksentievskaya village, the river Koloshma , riffle, stony substrate, 60°04'73''N, 35°31'36''E, 8 September 2004, A. Bobrov s. n. (holotype IBIW!, Fig. 3 , isotypes H!, IBIW!, KRA!, LE!, PRA!) .

Perennial aquatic plant up to 1(–1.5) m long. Rhizome short, slender, up to 2 mm in diameter. Stem slender, 1–2.2 mm in diameter, slightly compressed, shallowly grooved, unbranched to weakly branched; nodal glands absent. Submerged leaves near the base of stem reduced to phyllodes, otherwise with the distinct lamina (100–)120– 250(–310) mm long, 2–4(–5) mm wide, (20–)25–125(–155) times as long as wide, sessile, translucent, pale brown or yellow green when young, dark olive green when mature, consistently with a reddish tinge, becoming dark when dried, broadly linear, acute or slightly obtuse at the apex, entire and plane at the margin; midrib bordered on each side by a wide band of lacunae 3–7 cell wide, lateral veins 1–3 on each side, 1 of them more prominent than others, frequently bordered by narrow band of lacunae 1–2 cell wide. Transitional leaves similar to submersed ones but with shorter and wider lamina, 100–150 mm long, 4–6 mm wide, 17–38 times as long as wide, linear-lanceolate, broadest above the middle. Floating leaves rarely present, with the lamina 40–50 mm long, 6–8 mm wide, 6–8 times as long as wide, opaque, subcoriaceous, yellow green when young, dark olive green when mature, consistently with a reddish tinge, narrowly oblong-elliptical, gradually tapering to the wide petiole, acute or slightly obtuse at the apex, entire and plane at the margin; lateral veins 2–3 on each side; petioles 50–90 mm long, 2–3 mm wide. Leaves very gradually getting wider starting from phyllodes at the base, through submerged and transitional, up to floating in the upper part. Stipules 20–40(– 57) mm long, convolute to shortly connate at the base, translucent, colorless with a greenish or reddish tinge, rounded to obtuse at the apex, decaying early, with 2 more prominent and darker veins which not forming distinct ribs. Inflorescences rarely developed, 6–7 mm long, 4–6 mm wide; peduncles 34–65 mm long, as thick as a stem. Flowers scanty, in contiguous spikes, with 4 carpels. Flowering time from August to September. Fruits not seen, presumably not developing.

Stem anatomy: —Stele of oblong type, with formula of the main bundles 1, 2, 1 and additional, small bundles around; endodermis of O-U-type with weakly thickened cell walls; cortical bundles present, in one circle; subepidermal bundles present; pseudohypodermis present, 1-layered.

Distribution and habitat:— Potamogeton × clandestinus is known only from three rivers belonging to one river system. The system comprises the rivers Koloshma, Nozhema and the river Suda which is formed below the junction of the first two. The new hybrid grows in the lower parts of the rivers Koloshma and Nozhema as well as in the beginning of the river Suda ( Fig. 1 ). Along the river Suda P. × clandestinus spreads from its headwaters up to the middle of its course. In total this hybrid was recorded in eight localities (see list of specimens provided below), with the greatest concentration of patches around the junction of the aforementioned rivers.

Potamogeton × clandestinus prefers fast flowing water, it is significantly more abundant in riffles and rapids. It grows at a current velocity of 0.1–0.9(–1.2) m/s and at a depth of 0.1–0.8 m, on a solid substrate with pebbles, boulders, limestone, rarely with admixtures of sand. At the localities the water temperature is low because all three rivers are abundantly fed with springs. Even during the warmest period of the growing season the water temperature rarely reaches 16–18°C. Only in the lowermost locality of P. × clandestinus (the river Suda, Porog village) the water temperature 21°C has been registered.

The studied river system has headwaters originating from the small lakes at the Vepsovskaya Hills. This is a moraine height with hilly-ridge relief and with a large number of lakes and bogs formed after the last Valdai glaciation ( Yablokov 1973, Vorobiyov 2007). Carboniferous limestone bedrocks reaching the surface here in many places are cutted by the river courses what is reflected in the chemical parameters of their water. Water sampled from the localities of P. × clandestinus has low mineralization (119–308 mg /l), low total hardness (1.4–3.8 meq/l), neutral to weakly alkaline pH (7–8.7), with a dominance of hydrocarbonate ions (90–236 mg / l) and a high content of calcium ions (16–51 mg /l). The water is of the hydrocarbonate-calcium type, transparent with yellowish and brownish tinge (colority 100–200 degrees). The rivers is clean (oligo-β- mezosaprobic), oxygen-rich, with a low content of organic matter (oligo-mezotrophic).

Etymology:—The taxon’s epithet refers to the origin of the hybrid which is very difficult to recognize based on morphological characters. Potamogeton × clandestinus remained undetermined for almost ten years since its first finding.

Additional specimens examined (paratypes):— RUSSIA. Vologda reg., Babaevo distr., the river Koloshma: upstream from Kijno village , rapids, stony substrate, 11 July 2002, A. Bobrov, E. Chemeris s. n. (IBIW!); Aksentievskaya village , riffle, 12 July 2003, A. Bobrov s. n. (IBIW!). The river Nozhema: vicinity of Kijno village , rapids, stony substrate, 10 July 2002, A. Bobrov, E. Chemeris s. n. (IBIW!); ibid., rapids, 12 July 2003, A. Bobrov s. n. (IBIW!); Nizhnyaya Nozhema village , riffle, stony substrate, 60°06'44''N, 35°47'36''E, 3 June 2005, A. Bobrov, E. Chemeris s. n. (IBIW!); ibid., rapids, stony substrate, 8 August 2005, A. Bobrov, E. Chemeris s. n. (IBIW!); ibid., rapids, stony substrate (boulders, pebble), 20 June 2008, A. Bobrov, E. Chemeris, D. Philippov s. n. (IBIW!, Fig. 5 ); ibid., rapids, stony substrate (boulders, pebble), 8 July 2012, A. Bobrov, A. Sharapov s. n. (IBIW!, KRA 410485!). The river Suda: vicinity of Kobelyovo village , riffle, stony substrate, 10 July 2002, A. Bobrov, E. Chemeris s. n. (IBIW!); upstream from Maloe Borisovo village , riffle, 11 July 2003, A. Bobrov s. n. (IBIW!); Kyabelevo village , rapids, boulders and limestone, 60°01'43''N, 35°46'17''E, 9 August 2005, A. Bobrov, E. Chemeris s. n. (IBIW!, Fig. 4 ); ibid., rapids, stony substrate (boulders, pebble, limestone), 19 June 2008, A. Bobrov, E. Chemeris, D. Philippov s. n. (IBIW!); ibid., rapids, stony substrate (boulders, pebble, limestone), 7 July 2012, A. Bobrov, A. Sharapov s. n. (IBIW!, KRA 410484!). Kadui distr. , the river Suda : Porog village , on the edge of rapids, on flow, at limestone with sand, 59°35'10''N, 36°27'06''E, 6 July 2006, A. Bobrov, E. Chemeris s. n. (IBIW!) .

Figures

FIGURE 1. Localities of Potamogeton ×clandestinus in the Vologda region (Russia). Black triangle denotes the type locality.

FIGURE 3. Holotype of Potamogeton ×clandestinus (IBIW) from the river Koloshma (Aksentievskaya village, 2004, Vologda region, Russia).

FIGURE 4. Mature plant of Potamogeton ×clandestinus (IBIW) from the river Suda (Kyabelevo village, 2005, Vologda region, Russia). A. Shoot. B. Upper part with inflorescence. C. Floating leaves.

FIGURE 5. Young plant of Potamogeton ×clandestinus (IBIW) with characteristic long, linear submersed leaves (the river Nozhema, Nizhnyaya Nozhema village, 2008, Vologda region, Russia).