Introduction 61

Sect. 9. Hypericum 61

Subdivision 61

Characters and variation 61

Distribution and evolution 62

Sect. 9. Hypericum subsect. 1. Hypericum series 1. Hypericum 62

Characters and variation 62

Hybrids 64

Distribution and evolution 65

Systematic treatment 66

Sect. 9. Hypericum 66

Sect. 9. Hypericum subsect. 1. Hypericum series 1. Hypericum 67

References 119

Systematic index 121

The subdivision of the large sect. 9. Hypericum and four of its segregated sections having been treated in Part 4(1), Part 4(2) is concerned with those members of sect. 9, viz. Hypericum sensu stricto, in which the stem internodes have glandiferous raised lines – subsect. Hypericum series Hypericum. The series comprises 11 species and can be divided into (i) a group centred in Europe and the Mediterranean (4 species) and (ii) one centred in north-east Asia (6 species), one species of which is confined to western North America and another has spread westward into Europe. The remaining species (H. perforatum) is morphologically and geographically intermediate between two taxa, one from each group, and behaves as an allotetraploid hybrid. It is divided into four subspecies: subspp. perforatum, songaricum (Ledeb. ex Rchb.) N. Robson stat. nov., veronense (Schrank) H. Lindb. and chinense N. Robson subsp. nov. The hybrids of H. perforatum are treated in detail and include H. × desetangsii nothosubsp. balcanicum N. Robson, nothosubsp. nov. (H. maculatum subsp. immaculatum × perforatum). Other new hybrids proposed are: H. × laschii nothoforma froelichii N. Robson, nothoforma nov. (H. maculatum subsp. obtusiusculum × tetrapterum), H. undulatum × tetrapterum and H. elegans × perforatum.