Herbarium or botany-related seminars occur in many campus organizations. Here are links to the schedules for ones that frequently have sessions of particular interest to botanists:

Night at the Conservatory Lecture Series [https://www.plb.ucdavis.edu/news/night-conservatory-lecture-series]

Plant Sciences Seminars [https://www.plantsciences.ucdavis.edu/plant-sciences-seminars]

Evolution and Ecology Seminars [https://eve.ucdavis.edu/EVE%20Seminar]

Plant Biology Graduate Group Seminars

[https://biology.ucdavis.edu/event-category/plant-biology-graduate-group-seminar-series]