Photoperiodic Flowering Induction In Carex pensylvanica Lam

Carex pensylvanica (Pennsylvania sedge) is native to upland forests and savannas in the eastern half of North America and has horticultural utility as a groundcover for dry, shady areas. For landscape and restoration projects, it would be desirable to directly sow achenes instead of using vegetative propagules. However, C. pensylvanica typically has low achene production in its native habitat. As a first step in improving achene production, we studied the environmental factors influencing floral induction and initiation. In the first experiment, half of the plants were vernalized (4 °C) for 12 weeks under either 8 or 16 hour photoperiods. The remaining nonvernalized plants were subjected to either 8 or 16 hour photoperiods at 22 °C. All plants were exposed to irradiance levels of 200 umol·m^-2s^-1.  After the initial 12 week treatment, plants were held for an additional 8 weeks under either 8 or 16 hour photoperiods at 22 °C. All combinations of treatments were tested. In a second experiment, plants were exposed to 6, 8, 10, 12, or 14 hour photoperiods (22 °C, irradiance of 300 µmol·m^-2s^-1) for ten weeks. Data collected for both experiments included days to visible bud, first anthesis, and number of reproductive culms. The first experiment showed that C. pensylvanica is an obligate short day plant and that vernalization does not accelerate flowering. In the second experiment, 100% of plants flowered under 6, 8, 10, and 12 hour photoperiods; however, flowering was completely inhibited under the 14 hour photoperiod. Therefore, environmental conditions for production of achenes can be optimized.