Is not (just) unseen, is unclassified. Recognized as different stuff. Everybody going to a coastal area in the west coast of US had seen Western gulls. The spe

Is not (just) unseen, is unclassified. Recognized as different stuff. Everybody going to a coastal area in the west coast of US had seen Western gulls. The species split in the last decades by genetic analysis. Now we have western gulls and yellow-footed gulls. Same history with the European Herring gull and the Caspian gull. If you can still find a new species of big bird in California or Europe, hidden in plain sight, why not a shrub or a tree? There are plenty of ornithologists and much less people interested in botany, (not to mention virus, bacteria or fungus) Several hybrids can become species also. Plants are clonal, so non fertile hybrids can still multiply and eventually became fertile. There are many species complex in trees that are really arcane. Oaks or Willows for example. Lots and lots of plants have changed its taxonomy in the last ten years.