Ex situ phenology of Zizania texana, an endangered aquatic macrophyte, under different water velocities

Abstract

Texas wild rice (Zizania texana Hitchc.; TWR) is an endangered aquatic macrophyte limited to a 5 km stretch in the upper reach of the San Marcos River in Texas, USA. This study examined the phenology of TWR under different water velocities ex situ over 24 months. The results indicate that TWR exhibits fast initial growth rates of 0.4 m d−1 in total leaf length at 14 weeks in water velocities of 0.4 m s−1. The macrophyte exhibits a plastic reproduction system utilizing both sexual and asexual propagules. Differential development of the pistillate and staminate spikelets prevent self-fertilization and enhances genetic diversity. Plants in slower water velocities produced greater number of flowers and tillers compared to higher water velocities. Seed production was variable among flows but greater in lower water velocities. No difference was detected for seed germination among water velocities which averaged > 57% at 30 days and > 80% at 60 days. The high amount of seeds and tillers produced per plants indicate TWR exhibits reproductive plasticity possibly due to evolving under extreme floods and droughts. At 24 months, TWR allocated greater amounts of biomass to its roots compared to shoots regardless of water velocity which may provide further evidence of an evolutionary function to survive extreme flow conditions by establishing a deep root system.