Taxonomy and selection of Cephalotaxus Sieb. et Zucc.

摘要

Cephalotaxus Sieb. et Zucc. species are needle evergreens offering the aesthetic qualities of Taxus L., yew, yet are heat and drought tolerant, sun and shade adaptable, and resistant to deer browsing. They are adaptable to nursery and garden cultivation in USDA hardiness zones 5(6) to 9. Unfortunately, the nomenclature and taxonomy of the various taxa in the horticultural trade are frequently confused and the plants are slow to grow, which limits supplies and popularity. This research will address these problems.; The chloroplast gene rbcL of Cephalotaxus, which has been sequenced and utilized for determining species relationships and AFLP technique was applied to taxon discrimination and genetic variation. The seven species in the commercial trade were examined and only three distinct sequences were found. Sequence data, an concert with morphological and horticultural characteristics, suggest that only three species (instead of seven) currently listed in the horticultural trade should be accepted, which are C. harringtonia (including C. drupacea, C. koreana, and C. wilsoniana), C. fortunei (including C. sinensis), and C. oliveri. AFLP data supported the above conclusion and showed that C. sinensis is a hybrid species. For taxa subordinate to the species levels, the clustering results with reference to morphological characteristics indicated that four varieties and eight cultivars should be accepted. Practically, this work reduces the confusion relative to cultivated Cephalotaxus taxa. Furthermore, we recommend the use of rbcL sequencing to distinguish other morphologically homogeneous species and AFLP technique to discriminate taxa under the species level.; A total of 90 accessions representing 40 taxa was collected from around the world and grown at the University of Georgia campus for evaluation and selection. Based on their growth rates, appearance, and performance, two new cultivars (C. harringtonia 'Goodyear' and C. harringtonia 'McCorkle') and two existing cultivars (C. fortunei 'Prostrate Spreader' and C. harringtonia 'Prostrata') were selected for their medium to fast growth rates. These taxa have great potential for mass production by the nursery industry.