VOL. XVIII. (3) NOTES ON HELOSCIADIUM 231 



NOTES ON HELOSCIADIUM 



BY 

 Rev. H. J. RIDDELSDELL, M.A. 



Helosciadium is a genus of umbelliferous plants, very 

 closely allied to Apium, the common Celery, and often included 

 in one genus with it. It is represented in the British Isles by 

 four species only, of which one has but doubtful claims to 

 specific rank, as it is (in all probabiUty) a hybrid between two 

 other species. Like the Celery, all our Helosciadiunis are 

 normally waterside or water-plants, though they are often to 

 be found in spots temporarily dried up ; this last fact has an 

 important bearing upon the contents of this paper. 



Botanically, the group is characterised, among the Vm- 

 belliferoe, by having the sutural side of the seed flat {i.e., the 

 side by which one half of the complete fruit is united to the 

 other half) ; by having compound umbels, each consisting 

 of a number of rays or umbellules, the number of which is 

 in Helosciadium sometimes of critical importance ; its carpels 

 (or half-fruits) have only five true ridges on the surface, and 

 ttieir sutural sides are about as large as each of the other four 

 sides. As often happens in Umhelliferce, the flowers are very 

 small, with practically no calyx, and with tiny round white 

 or cream coloured petals with an acute point. 



H. nodifiorum, Water-parsnep or Marshwort, is the 

 species of this group which is most famiUar to us down South : 

 and, no doubt, in Britain as a whole it supphes a far larger 

 number of individual plants, as well as localities, than does 

 H. inundatum. But the distribution is pecuUar : it thins out 

 Northward very much, being of Hmited occurrence in Scotland. 

 H. inundatum thus actually occurs in more counties (in the 

 proportion of about 6 to 5) than the commoner species, for 

 it is the more widespread of the two. 



A lengthy technical description is unnecessary, for H. 

 nodifiorum is familiar as a ditch plant. It is often mistaken 



