Biosystematics and phenology of Alnus maritima (Betulaceae).

摘要

Alnus maritima (Marsh.) Muhl. ex Nutt. (seaside alder) is a rare woody plant species found naturally in only three small disjunct populations in the United States. Concern for the conservation of A. maritima and questions regarding the proper classification of its disjunct populations have generated a need for information concerning its ecology and biosystematics, while growing interest in the use of A. maritima in managed landscapes has demonstrated the need for information concerning its ecophysiology and landscape fitness. My first objective was to recount the taxonomic and horticultural history of A. maritima and to report on its current landscape usage and cultivation. Although it has received little attention from horticulturists since its introduction into cultivation over 100 years ago, A. maritima is now being recognized as a stress-resistant large shrub or small tree. My second objective was to derive the infraspecific systematics of A. maritima by morphometric analysis and to classify the three disjunct populations properly. Taxonomic distances were compatible with the modern definition of subspecies, and the subspecific epithets oklahomensis, georgiensis, and maritima were given the three taxa. My third objective was to characterize the molecular systematics of A. maritima according to ISSR polymorphisms. The molecular phylogeny of eight species of Alnus confirmed that A. maritima is most closely related to the other members of subg. Clethropsis and was the first member of its subgenus to diverge. At the infraspecific level, molecular and morphometric phylogenies agreed and showed that subsp. oklahomensis was the first to diverge. My fourth objective was to characterize the cold hardiness of A. maritima in native habitats and in colder climates. Analyses showed that the subspecies are similar in cold hardiness, that plants from all three subspecies can survive mid-winter extremes as low as −80°C, and that cold acclimation differs between plants grown in colder climates and those in native habitats. Results from these studies support the theory that A. maritima originated in Asia, migrated into North America across the Bering land bridge, and was established over a large range before being forced into its present meager distribution.