Youngia

Abstract: Cladistic analysis of the trilobite subfamily Acanthoparyphinae Whittington and Evitt, 1954, yields an explicit hypothesis of relationship for the group. All Silurian species together form a robustly supported monophylum including the genera Hyrokybe Lane, 1972, Parayoungia Chatterton and Perry, 1984, and Youngia Lindstrom, 1885. Sister to this is the Ordovician type species of Acanthoparypha Whittington and Evitt, 1954. Remaining species that have historically been assigned to either Acanthoparypha or Pandaspinapyga Esker and Levin, 1964, form a rather labile paraphylum. Nevertheless, the entire group thus identified is definitely monophyletic, and supported by several prominent synapomorphic character-states. The basal structure and basal node of the subfamily are more difficult to assess. The relationships of the genera Hammannopyge Pribyl, Vanek, and Pek, 1985, Holia Bradley, 1930, and Nieszkowskia Schmidt, 1881, need to be addressed within the wider context of the family as a whole. The traditional assignment of Holia to the acanthoparyphines is followed. Wenlock acanthoparyphines from the Cape Phillips Formation of the central Canadian Arctic islands include several species of Hyrokybe and Parayoungia. They are similar to, and in one case conspecific with, coeval forms to the southwest in the southern Mackenzie Mountains. Five species are new: Holia glabra, Hyrokybe lightfooti, Hyrokybe youngi, Hyrokybe mitchellae, and Parayoungia mclaughlini. At least four other potentially new species are reported in open nomenclature.

Abstract: The EtOAc extract of Youngia koidzumiana significantly inhibited the diacylglycerol acyltransferase (DGAT) from rat liver microsomes. Bioactivity-guided fractionation led to the isolation of nine compounds, the structures of which were established using physicochemical and spectral data. Of the isolated compounds, oleanolic acid (2), methyl ursolate (7) and corosolic aicd (8) inhibited DGAT, with IC50 values of 31.7, 26.4, and 44.3 microM, respectively. However, sesquiterpenoids showed only weak inhibitory effects toward DGAT.

Abstract: The pollen morphology of 15 species representing four sections of Youngia and 11 species from six other genera of the tribe Cichorieae was investigated. Measurements and observations were conducted through scanning electron microscopy. This study aims to provide new and useful information regarding the extent of pollen morphological diversity within the genus Youngia and related genera in the tribe Cichorieae and thus to contribute to a better understanding of the taxonomy and evolution of these groups. Six pollen types, distinguished primarily by the number of apertures and spines in the polar region, are described. Palynological characters are not useful for the delimitation of Youngia and its closely related genera Crepidiastrum , Ixeridium , and Crepis at the generic level, and did not fully resolve the relationships between the groups. The distinction of Faberia from the other members of the subtribe Crepidinae is supported by the pollen characters. Pollen morphology also did not support that Youngia sect. Desiphylum sensu Babcock and Stebbins may be separated at the generic level either as Tibetoseris or Pseudoyoungia . Four pollen types were found in Youngia s.l., i.e. Y. racemifera type, Y. japonica type, Y. prattii type and Y. sericea type, which partly reflect the sectional classification of Youngia sensu Babcock and Stebbins. The systematic position of Y. racemifera should be reconsidered according to pollen characters. The pollen data suggest that Y. sect. Mesomeris is not monophyletic, and the relationships of its species require further examination.