Specimens of P. brachystoma and its related species A holotype of P. brachystoma (Farrer 1635, E, https://data.rbge.org.uk/herb/E00024386) B isotype of P. polonensis (Kingdon-Ward 8388, E, https://data.rbge.org.uk/herb/E00024403) C isosyntype of P. prenantha subsp. prenantha (G. King’s, E, https://data.rbge.org.uk/herb/E00259794) D type of P. prenantha subsp. morsheadiana (Ward, F. K. 5858, K, http://apps.kew.org/herb/K000750095) E holotype of P. serratifolia (Forrest 1816, E, https://data.rbge.org.uk/herb/E00024076) F syntype of P. melanodonta (Kingdon-Ward 7042, E, https://data.rbge.org.uk/herb/E00531116).