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In Minnesota , Wheeler et al. ( 1985 ) found species characteristic of oak openings and barrens to be abundant ( based on herbarium collections ) although most remaining areas of openings and barrens are small . With regard to the illustrations of each species , those for which no photo is given ( 47 out of 228 species , or over 20 % ) , such as Trifolium acaule , T. breweri , T. siskiyouense , and so on ) could have been represented by photos made from herbarium specimens . If you have used a wildflower guide , you've used information originally taken from herbarium specimens . Pollen reference collections , in part made from herbarium specimens , are important resources for pollen identification . Are the answers to those questions held by herbarium specimens ?