THE MONOCOTYLEDONES 



1975 



interest because of the undoubted general resemblance to the Ranuncu- 

 laceae. Whether this similarity is due to a true phylogenetic relationship or 

 produced as a result of parallel evolution is a matter not yet easily settled, 

 but we shall later compare some of the characters of the two families. 



In the British Flora the family is represented by two well-known 

 plants, Alisma plant ago-aquatica (Fig. 1905) (Water Plantain) and Sagittaria 

 sagittifolia (Arrowhead), while in 

 addition Eltsma nutans, a delicate 

 little European species, is found 

 rarely in British fresh waters. Dama- 

 suniiim stellatum (Thrum Wort) is a 

 western Mediterranean plant which 

 is sometimes met with in ditches and 

 ponds in southern England. 



The plants are rhizomatous with 

 large radicle leaves which may be 

 erect, floating or submerged and are 

 dilTerently shaped according to their 

 position. The veins are parallel with 

 the margins and convergent at the 

 apex, with transverse nerves, often 

 close and parallel. There are small 

 scales in the leaf axils, known as in- 

 travaginal scales. Laticiferous tissue 

 may be present. 



The inflorescence is usually much branched, the primary branching 

 being racemose while the secondary branching is cymose. The individual 

 flowers are often whorled. 



Fig. 1905. — Alisma plantai^o-aqiiatirn. 

 Water Plantain. Flower, enlarged 

 X 4. 



Fig. igo6. — Floral diagram of 

 Alismaceae. 



Fig. 1907. — Alisma plantaao- 

 aqtiatica. Flower in section 

 showing calyx and corolla. 



The flowers (Fig. 1906) are hermaphrodite or sometimes monoecious, 

 actinomorphic and possess distinct calyx and corolla (Fig. 1907). 



2G* 



