Selaginellaceaey Isoetaceae 3 



Suborder 2. LiGULATAE. Heterosporous forms with 

 ligule. 



Family Selaginellaceae. Erect or suberect herbs. 

 Haplostelic or polystelic. Rhizophores often arising 

 exogenously and bearing endogenous roots. Leaves 

 rarely spiral, more often in two dorsal and two ventral 

 rows. Sporophylls aggregated in cones, which contain 

 both macro- and microsporophylls. Macrosporangia tj-pi- 

 cally with four macrospores, microsporangia with numerous 

 microspores. Embryo with two cotyledons. 



Only genus : Selaginella. 



(The British species is haplostelic with spirally ar- 

 ranged leaves.) 



Order 2. Isoetales. Submerged subaquatic or 

 terrestrial plants with very short unbranched fleshy 

 stems, bearing alternating whorls of sterile and fertile, 

 elongated, subulate or filiform leaves. Stele with anoma- 

 lous secondary thickening. Sporangia bulky, single, in 

 pit on adaxial face of leaf base adjoining the ligule. 

 Macrosporangia with numerous macrospores, microspore 

 angia with very numerous microspores. Sterile trabeculae 

 between the spores. Spermatozoids multiciliate. 



Only family: IsOETACEAE. 



Only genus : Isoetes. 



Class 3. FILICARIAE. Leaves almost always large 

 in relation to the stem, often highly compound, mostly 

 with circinate vernation. Stem haplostelic, solenostelicf 



t Solenostele. A stele in which the vascular tissue is arranged 

 in a hollow cylinder of xylem lined within and without by phloem, 

 pericycle and endodermis, and the continuity of which is inter- 

 rupted by leaf-gaps which do not overlap (Tansley, I.e.). 



1—2 



