302 ARROWHEAD ORDER 



NAIAS Linne 1753 NAIAS 

 (Gr. naias, water-nymph, from, the habitat) 



Perianth of the staminate flower double, outer entire or 4-horned, the 

 inner hyaline, adhering to the single anther, pistillate flower a single ovary 

 with 2-4 stigmas, carpels solitary ; flowers monoecious or dioecious, solitary, 

 axillary; leaves usually opposite or whorled, sheathing at base; submerged 

 aquatic. 



1. Leaves tapering to a point, 12-25 mm. long, 1-2 



mm. wide N. flexilis 



2. Leaves rather obtuse at tip, 1-2 cm. long, .5-1 



mm. wide N. guadaloupensis 



POTAMOGETON Linne 1753 PONDWEED 



(Gr. potamos, river, geiton, neighbor, from the habitat) 



PL 44, fig. 1. 



. Perianth of 4 parts, stamens 4, pistils 4, separate, fruit of 4 1-seeded 

 drupelets ; flowers perfect, green or red, in spikes ; leaves alternate or the 

 uppermost opposite, usually of 2 kinds, submerged and floating; submerged 

 or floating aquatic. 



1. Stems with both floating and submerged leaves 



a. Submerged leaves with the flat blade present 



(1) Submerged leaves of 2 forms, elliptic and 



lanceolate P. amplifolius 



(2) Submerged leaves alike 



(a) Submerged leaves linear 



x. Leaves thread-like with attached stip- 

 ules P. diverslfolius 

 y. Leaves lance-linear with free stipules P.-heterophyllus 



(b) Submerged leaves not linear 



x. Some or all of the leaves petioled 

 (x) Upper leaves petioled, lower ses- 

 sile; floating leaves spatulate to 

 oblanceolate P. alpinus 



(y) All the leaves petioled; floating 



leaves elliptic P. lonchites 



y. All the leaves sessile or short-petioled P. Zizii 



b. Submerged leaves without the usual flat blade ; 



floating leaves ovate to elliptic P. ndtans 



2. Stems without floating leaves 

 a. Leaves lanceolate to ovate 



(1) Leaves heart-shaped and perfoliate P. perfolidtus 



