摘要:

The members of the genusSonchussubgenusDendrosonchusare woody perennials possessing the pachycaul construction which has been proposed as ancestral to that of modern trees and herbs. The endemic flora of Macaronesia, particularly the Canary Islands, is generally considered to be a Tertiary relict, although an opposing view concerning woody plants of island floras has recently been expressed. The anatomy ofDendrosonchusis examined and trends of evolution can be interpreted from the vessel elements of the secondary xylem. With the use of the length to breadth ratios of vessel elements a gradual trend from primitive to derived is illustrated for the members of each of the two sections ofDendrosonchus, which are considered to have evolved in parallel. The wood rays, features of the cypsela and stem anatomy are also shown to be useful in elucidating the evolution of a small, closely related group of plants.Sonchus arboreusin the sectionAtalanthusandS. brachylobusin the sectionDendrosonchusare similar to the two ancestral types proposed for the subgenus. The most derived species are considered to beS. pinnatussubsp.palmensisin the sectionAtalanthusandS. acaulisin the sectionDendrosonchus.The ancestral type for the genus is considered to have been woody and probably of theDendrosonchustype.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1978.tb01815.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1978.tb01816.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1978.tb01817.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY