464 Eaton: Pteridophytes observed in Florida 



Acrostichum excelsum Maxon, Proc. Biol. Soc. 



Wash. 18: 224. 1905 



(A. lomarioides Jenman) 



This is the largest fern growing in the United States. The 

 species has been confused with A. aitrctun, from which it is most 

 readily distinguished by its larger size, its close-set pinnae and the 

 fact that all the pinnae of the fertile fronds bear sporangia. The 

 stipes lack the spinous processes of A. aurctun, and the under side 

 of the sterile pinnae in all my specimens but one is covered with 

 very short bristles. The basal areolations are not enlarged and 

 are not parallel to the midrib ; the primary veins spread at a 

 greater angle, and are often parallel, and the connecting veinlets 

 are often at right angles to them, the resulting areolations being 



more or less rectangular. The rootstocks are not infrequently 

 5-9 dm. long, 7-10 cm. in diameter, horizontal with an ascending 

 tip, or assurgent, bearing numerous thick cord-like roots. The 

 fronds may be 30-33 dm. long and 7.5 dm. broad, the stipes 2.5 

 cm. or more in diameter. Usually, especially in sunlight, the pin- 

 nae are abruptly ascending with the upper side facing the rachis. 

 This habit is also seen in A. aureum and is not universal in either 

 species. It is not confined to brackish shores, but grows well in 

 the swamp hammocks bordering streams, less frequently in those 

 of the everglades and the cypress. Although often growing where 

 the water is fresh, it becomes scarce a short distance from the in- 

 fluence of salt water, and doubtless disappears entirely a few miles 

 away from the sea. Not infrequently the pinnae bear one to sev- 

 eral simple or forked lobes at the bases, on one or both sides, 

 each lobe with a midrib that in the largest examples is branched 

 from the main vein, but in the smaller ones melts away into the 

 ordinary nerves before reaching it. Although several fronds of 



fc> •*• ""nv/wg 



this structure may often be found on a single plant, the occurrence 

 is simply accidental and the form may be known as forma lobatum* 



Stenochlaena J. Smith 



Fronds dimorphous, the fertile pinnae contracted, soriferous 

 all over the back as in Acrostichum, the thin membranaceous 

 margin often re volute. 



