Callitriche L.

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1972, Flora Europaea. Volume 3. Diapensiacea to Myoporaceae, Cambridge: Cambridge University Press : 123-124

1. Callitriche L. 3

Submerged, amphibious or terrestrial herbs, with axillary glandular scales, and sometimes with peltate cauline hairs, otherwise glabrous. Leaves simple. Flowers solitary, or 1 male and 1 female flower in the same leaf-axil. Bracteoles 0 or 2 (in European species), membranous. Anthers reniform. Mericarps with rounded, keeled or winged margin.

5 well-defined groups of species can be recognized in Europe, and hybridization between species of different groups is unknown. The amphibious species are very variable, and identification is made difficult because of the vegetative similarity of different species when growing in similar habitats.

Ripe fruits are essential for identification; the anatomical details of the mericarps can easily be observed (in European species) after stripping off the outer layer of cells. In 5-13

peltate hairs are present on the stems; their shape and the number of cells in the disc are of diagnostic importance. All species except 1 -3 can occur in the terrestrial form on mud; the habitat given is for the aquatic form. The plants are usually annual, but the life-cycle depends on climatic factors, and most of the species can be perennial in some part of their range.

Literature: H. D. Schotsman in P. Jovet, Flore de France 1. Paris. 1967.

1 Terrestrial

2 Fruit c. 0-6 mm, wider than long

3 Mericarps thicker at base than apex 12. peploides 3 Mericarps of equal thickness throughout 13. terrestris 2 Fruit O'8 mm or more, suborbicular or longer than wide

4 Mericarps not winged (sometimes weakly keeled)

5 Fruit 1-5 mm, elliptical; mericarps with rounded, scarcely distinct margin; pollen-grains oblong-ellipsoid or slightly reniform 6. obtusangula 5 Fruit 0-8-1-2 mm, suborbicular or slightly oblong; mericarps with distinct but obtuse margin; pollen-grains shortly ellipsoid or subglobose 7. cophocarpa 4 Mericarps winged

6 Mericarps winged only at apex; fruit obovate (rarely elliptical) 9. palustris 6 Mericarps winged from base to apex; fruit suborbicular or slightly longer than wide

7 Persistent styles deflexed and appressed to sides of fruit

8 Fruit subsessile or very rarely shortly stalked 10. hamulata 8 Fruit with long stalk up to 13 mm 11. brutia 7 Persistent styles erect or recurved, not appressed to sides of fruit

9 Styles recurved; leaves pale green, broadly elliptical or suborbicular; fruit pale brownish, with broadly winged mericarps 5. stagnalis 9 Styles erect or patent; leaves dark green, elliptical; fruit brown, usually with narrowly winged mericarps

1 Aquatic 8- Platycarpa 10 All leaves submerged

11Leaves not transparent; wing of mericarp with 1 row of cells; persistent styles appressed to sides of fruit

12 Leaves expanded at apex, with deep, crescentic emargination 10. hamulata 12 Leaves not widened at apex, often with asymmetrical emargination 11. brutia 11 Leaves transparent; wing of mericarp, if present, with at least 2 rows of cells; styles deciduous

13 Fruit suborbicular 1. hermaphroditica 13 Fruit wider than long

14 Wing of mericarp narrow or absent; fruit c. 1-5 mm wide

2. truncata 14 Wing of mericarp wide; fruit 1-8-2-2 mm wide

15 Mericarps broadly reniform, with large seed; stellate thickenings present in cells of wall enclosing seed

3. pulchra 15 Mericarps almost semicircular, with small seed; stellate thickenings not present in cells of wall enclosing seed

4. lusitanica 10 Upper leaves spathulate, forming a floating or aerial rosette

16 Rosette aerial, raised above surface of water; submerged linear leaves and basal part of rosette-leaves transparent; fruit wider than long 4. lusitanica 16 Rosette floating; submerged leaves and basal part of rosetteleaves not transparent; fruit suborbicular or longer than wide

17 Flowers submerged; pollen-grains colourless; persistent styles appressed to sides of fruit

18 Usually iobust; fruit c. 1-4 mm wide, suborbicular; mericarps narrowly winged 10. hamulata 18 Slender; fruit 1-1-2 mm wide, usually longer than wide; mericarps often broadly winged 11. brutia Flowers aerial; pollen-grains yellow; persistent styles not appressed to side of fruit 19 Mericarps unwinged, sometimes weakly keeled

20 Fruit 1-5 mm, elliptical; mericarps with rounded, scarcely distinct margin; pollen-grains oblongellipsoid or slightly reniform 6. obtusangula

20 Fruit 0-8-1 -2 mm, suborbicular or slightly oblong, mericarps with distinct but obtuse margin; pollen-grains shortly ellipsoid or subglobose 7. cophocarpa

19 Mericarps winged

21 Mericarps winged only at apex; fruit l(-l-5)mm, obovate (rarely elliptical), blackish 9. palustris

21 Mericarps winged from base to apex; fruit 1-4-1-75 mm, suborbicular, brownish

22 Leaves pale green, narrowly elliptical when submerged; mericarps broadly winged 5. stagnalis

22 Leaves usually dark green, linear when submerged; mericarps narrowly winged 8. platycarpa (a) Always submerged. Leaves more or less linear, transparent. Cauline hairs absent. Flowers solitary. Bracteoles absent. Stamen erect before and after dehiscence, scarcely elongating; anther-wall with thin-walled cells; pollen-grains colourless, without exine. Wing of mericarp, if present, composed of one or more rows of polygonal cells. Basic chromosome number 3, 4.