The Marin Municipal Water District and the California Academy of Sciences are looking for people with an interest in botany, photography or data-gathering to help them catalog plant life in the Mount Tamalpais Watershed. Volunteers will be trained so they can join at least five botanists and two ecologists in a series of “bioblitzes” through August to collect observations and samples of life on Marin’s defining peak. At least 900 plant species are found in the 18,500 acres owned by the district. Last year’s bioblitz volunteers uncovered more than 300 kinds of plants, including 42 not previously collected in the watershed, and sent 200 samples to the Academy of Sciences herbarium in San Francisco’s Golden Gate Park. Andrea Williams, a vegetation ecologist with the water district, said the flora catalog is intended to give scientists a sense of how life in the watershed is changing and to raise public knowledge of science. “You can’t manage what you don’t understand,” Ms. Williams said. Mount Tam “is a biodiversity hotspot and needs an accurate and up-to-date catalogue of just how special it is.” Prospective volunteers can register for the mandatory Feb. 23 training session by calling (415) 945.1128 or by emailing email@example.com. An informational orientation will be held at the Academy of Sciences on Feb. 20.