Seed germination of two Everglades species, Cladium jamaicense and Typha domingensis

The germination requirements of Cladium jamaicense Crantz and Typha dominge nsis Pers. were studied under controlled conditions in the laboratory. Trea tments included six temperature regimes, (constant temperatures of 15, 20, 25, 30 degrees C, and two fluctuating day : night temperature regimes of 25 : 10 degrees C and 30 : 20 degrees C), two light levels (14 : 10 h light : dark photoperiod and 24 h dark environment), two substrates (peat and wate r) and two O-2 levels (atmospheric and low (4.34%) O-2 concentration) using a complete randomized block design. The average incubation period needed for seeds to germinate was shorter for T. domingenesis (1.1-19.5 days) than for C. jamaicense (26-46 days) and th e final germination percentage was higher for T. domingensis than for C. ja maicense (85 vs. 42 %). Cladium jamaicense only germinated with fluctuating temperatures whereas T. domingensis germinated at all temperature regimes. Light was required for T. domingensis seeds to germinate, whereas C. jamai cense could germinate at a reduced rate in the dark. Peat substrate had a p ositive effect on germination in both species. Peat substrate shortened the incubation period for seeds of both species, enhanced germination of T. do mingensis, especially at low temperatures, and enhanced germination of C. j amaicense in the dark. Low oxygen availability did not influence the germin ation of C. jamaicense but enhanced germination of T. domingensis at low te mperatures. Although the two species differ significantly in their germinat ion requirements and responses to specific environmental conditions, germin ation of both these species was enhanced by environmental conditions typica l of exposed water saturated mudflats or sediment surfaces. Typha domingens is produces a large number of small seeds, which do not germinate when cove red by sediment. In contrast, C. jamaicense produces fewer and larger seeds , with resources able to support growth through a thin layer of sediment or detritus. (C)2000 Elsevier Science B.V. All rights reserved.