Germination of coastalplain honeycombhead (Balduina angustifolia) in response to photoperiod, temperature and gibberellic acid

Coastalplain honeycombhead (Balduina angustifolia) is underutilised in ecosystem restoration and pollinator conservation projects. Seeds collected from different populations throughout Florida, USA during 2007 and 2016-2018 were used in experiments that evaluated the effects of a 0 or 12-hour photoperiod, seasonal and standard temperatures, 0-5,000 ppm gibberellic acid (GA) or source population (northwest, central and south Florida) on seed germination. For central Florida seeds, germination was high (62-74%) in all seasonal temperatures except for summer (4%) and was not affected by photoperiod. Germination differed for two northwest populations and was higher in warm (35/25 and 30/20°C) temperatures compared with cool (25/15 and 20/10°C) temperatures (63-72% vs. 9-36%). In a one-year move-along experiment, germination was similar at all seasonal and constant temperatures for seeds from central, south-central and south Florida, while northwest Florida seeds had reduced germination under winter temperatures. Germination of northwest Florida seeds after exposure to GA increased for two of four and three of four populations for one year and five-day old seeds, respectively. There were different temperature requirements on a regional scale and different dormancy levels at a local scale for coastalplain honeycombhead.