The Center for Plant Diversity is a special facility within the Plant Sciences Department on the Davis campus of the University of California. Its main resource is the J.M. Tucker Herbarium, composed of 300,000 vascular plant specimens, 2,400 bryophyte specimens, 2,000 macroalga specimens, 1,700 lichen specimens, and 600 conifer cones. 

Our collections are world-wide in scope, but the geographic region that is the most complete is northern California. We have excellent collections of Poaceae (grasses - nearly one quarter of our collections are grasses) and Euphorbiaceae (spurges), and good collections of emblematic California genera, such as Navarretia, Clarkia, Trifolium, Quercus, and Arctostaphylos.

Our Logo

Our logo is a combination of a border of Crampton’s tuctoria (Tuctoria mucronata), a federally listed endangered vernal pool grass limited to Yolo and Solano Counties, surrounding an acorn of Quercus john-tuckeri, an oak endemic to California.

The Crampton’s tuctoria is emblematic of former herbarium Director Beecher Crampton who studied grasses and vernal pools and who originally described this species. The acorn is emblematic of former herbarium Director John Tucker, who studied oaks, and for whom this species is named.

History

The Center for Plant Diversity is an amalgamation of several early California collections and herbaria, including the former Botany Department Herbarium (founded at the University Farm in 1922 by W.W. Robbins), the Beecher Crampton Agronomy Department Herbarium (founded 1913 at UC Berkeley by Patrick B. Kennedy), a Vitis vinifera collection from California Agricultural Experiment stations (built over the period of 1895-1915 by Frederic T. Bioletti and Harold P. Olmo), and the Environmental Horticulture Herbarium (founded ca. 1970 by Andrew T. Leiser). 

Since its founding, it has expanded according to the varied research interests of its staff, finds by extension agents, farm advisors and its community of botanists. Prominent past contributors are: Beecher Crampton (grasses), Ellen Dean (Solanaceae, California flora), Jack Major (Alpine flora), James Nielson (Mayacamas Mts. flora), Dan Potter (Rosaceae, California flora), Edwin Laidlaw Smith (willows), G. Ledyard Stebbins (California flora) Dean Taylor (California flora), John Tucker (oaks), Shirley Tucker (lichens), Grady Webster (Euphorbiaceae), Charles Rick (tomatoes), and Joe DiTomaso, Fred Hrusa, June McCaskill (California weeds).

The collection continues to expand by 5-10,000 specimens per year. Recent major contributors include: Jack Alderson (Colusa County), Jim Andre (Mojave Desert), Glenn Clifton (California), Shane Hanofee (Sierra Nevada), Hannah Kang (northern California), Nick Jensen (Tejon Ranch), John McLaughlin (bryophytes of Henry Coe State Park), Robert Preston (California), Stephen Rae (California mosses), Jake Rugyt (Napa County).

More About the Founders

• Harold P. Olmo - https://fps.ucdavis.edu/grapebook/winebook.cfm?chap=HaroldOlmo
• John Tucker - https://video.ucdavis.edu/media/John+Tucker/0_8fa3dxfs
• Grady Webster - https://video.ucdavis.edu/media/Grady+Webster/0_k36bdg0k
• Bioletti - https://scalar.usc.edu/works/from-vine-to-wine/frederic-t-bioletti-university-of-california-berkeley-1865-1939

FAQs

• Where do our specimens come from?
• Our specimens are given to us by campus researchers, students, state or federal agency botanists, consultants, and anyone else who wishes to deposit their specimens.  We also have an active exchange program which allows us to exchange extra specimens with other herbaria.  Some of our specimens have come to us as "gifts for determination"; in this case, a researcher has given us the specimen in exchange for us identifying the specimen for them. We also do floristic surveys, where we collect and identify all the plants in a given area, such as a county or state park or preserve and create a list and a set of vouchers of those species.
• What do we do with the specimens when they come in?
• If the specimens are fresh, we dry them in plant presses in our drying oven for several days. If they are dry, they get frozen at -20°C for at least a week to kill any insect larvae that may be in them. Then we match the field data to the specimen and enter the data into our online database. We identify the plant if needed and then print the label. The label and the specimen go into a cabinet to wait for mounting on archival paper. 
• Who uses the Herbarium?
• Anyone may use our collections.  The herbarium is used primarily by students and researchers from this campus and elsewhere in the herbarium workroom.  Some faculty borrow specimens for teaching or demonstrations.  When this occurs, we place the specimens in protective covers to prevent damage.  We instruct our users in how to properly handle the specimens, how to prevent insect infestation, and how to limit destructive sampling.  
• How is the Herbarium used?
• Basic plant identification
  This is by far the most common reason that people consult our specimens.  During the process of identifying a plant to species, the final step should include comparing the unknown plant with an herbarium specimen.  Users either do this themselves, or they give us the unknown plant, and we assist them with the identification.
  
  Label data - especially location and date
  The information found on the labels of our specimens is just as valuable as the plants themselves.  Often we get inquiries for location data for species in our collection. In conjunction with the date of collection that is found on the label and the flower/fruiting state of the specimen, researchers can figure out exactly when to go to a particular location to find the species in flower or fruit. If enough herbarium specimens are consulted, researchers can also figure out the flowering and fruiting dates for a species over its entire range. 140,000 of our specimens (about half) have been databased, which means that their label data are available online for use in such analyses at the Consortium of California Herbaria/Jepson Herbarium website www.cch2.org
  
  Taxonomic studies
  Systematic botanists (also known as taxonomists or systematists) study the evolution and classification of plants.  As part of their studies, they examine herbarium specimens - both the plant and the label. They obtain locality and date data, so that they can plan the timing of their field work. They look at dried plant specimens, and measure numerous individuals. Dried specimens allow one to measure stems, leaves, and flowers; flowering specimens may yield pollen samples, fruiting specimens may have seeds that could restore extinct populations; and leaf material might be used for DNA analysis. 
  
  Systematists use the information they gather from herbarium specimens to write taxonomic treatments of species or groups of species. Taxonomic treatments describe species in detail, provide illustrations of new species, and include identification keys to all the species in the treatment.  In turn, these treatments are used as the basis of floras and identification manuals such as the Jepson Manual of Higher Plants of California.
  
  During the process of writing a taxonomic treatment, systematists often borrow specimens from other herbaria; this is called a loan.  When the borrower is finished with the loan, they annotate, or put their new identification on each specimen before returning the loan. Loaning our specimens to taxonomic experts is one way that we keep the names on our specimens up-to-date. 
  
  Other types of research
  As our specimens become digitized, imaged and available online, they are becoming widely used for other types of research projects. Current projects our specimens are involved in: looking at changes in phenology (flowering) over time as a signal of climate change, looking at changes in insect herbivory over time as a signal of climate change, looking for traces of crop pathogens (bacteria and viruses) over time.