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2. Babcock E. B.andG. L.Stebbins Jr.1937.The genus Youngia.Carnegie Inst. of Washington Publ. 484.
3. Palynology of the genus Tolpis Adanson (Compositae: Lactuceae);Blackmore S.;Pollen & Spores,1986
4. SUBGENERIC AND SECTIONAL NAMES: THEIR STARTING POINTS AND EARLY SOURCES