Research Accomplishment Reports 2007

Seed Germination Ecology of Hawaiian Montane Species

C. Baskin
Department of Plant and Soil Sciences

 

Project Description

The ultimate goal is to provide people who are propagating Hawaiian native species and/or those who are involved in habitat restoration and conservation with research-based information on dormancy-breaking and germination requirements of as many of the Hawaiian montane species as possible, including rare species such as some of the lobelioids. This information will enhance the ability of propagators to grow plants from seeds and of preservation managers to optimize conditions for seed survival, dormancy break, and germination in the natural habitat.

During 2007, laboratory studies were conducted on seeds of 20 species to determine their class of dormancy and to find ways to break dormancy. Seed dormancy has been broken in 15 of the species, and studies are in progress on the remaining five species to determine how to break dormancy. Also, studies have just been initiated on newly-collected seeds of six species. Additional species of Hawaiian lobelioids were studied, and all of them have seeds with underdeveloped physiologically dormant embryos (thus they have morphophysiological dormancy), confirming the results of a previous study (Can. J. Bot. 83: 1630-1637. 2006). This means the tiny (dwarf) seeds of the lobelioids have small embryos that must grow to a species-specific length inside the imbibe seed before the root can emerge from the seed. Also, the small embryo has physiological dormancy which must be broken, usually by long periods of warm, moist conditions. Other activities during 2007 include giving an invited keynote lecture at the Seed Ecology Meetings in Perth, Australia, on 10 September.

Impact

Based on results from studies on seeds of the Hawaiian lobelioids and on seeds of members of the gentian and campanula families collected in Kentucky, it became clear that some of the definitions used by Martin in his 1946 classical paper (Amer. Midl. Nat. 36: 513-660), especially for small seeds, probably needed to be revised. His classification system has 10 types of seeds based on embryo and endosperm characteristics and two additional types based on seed size: dwarf (0.3-2.0 mm) and micro (≤0.2 mm). Further, he listed 17 families and 12 genera (in five other families) as having dwarf seeds, but the discovery of morphophysiological dormancy in dwarf seeds of the Hawaiian lobelioids and members of the campanula and gentian families called his dwarf seed category into question. In his paper, Martin has 37 families with one to several small (0.3-2.0 mm)-seeded species that he did not list as being dwarf.

Comparison of Martin's dwarf families and the 37 small-seeded nondwarf families revealed no consistent differences between the two groups in endosperm texture, seed coat anatomy, embryo morphology, class of seed dormancy or phylogenetic position. Also, his dwarf seeds include a variety of embryo morphologies.

Consequently, the Martin key to seed types has been revised. The dwarf category has been removed and the micro category replaced by undifferentiated to reflect the state of the embryo in fresh seeds. Further, the key now includes linear fully developed, linear underdeveloped, spatulate fully developed and spatulate underdeveloped seed types, which Martin illustrated but did not include in his key.

In the revised key, all seeds are distinguished on the basis of embryo and endosperm characteristics. Now, it is possible for people to more clearly communicate information about seeds, and especially small seeds. Thus, it has become clear that, depending on the species and whether the embryo must grow (or not) prior to germination, several kinds of dormancy may be found in small seeds.

Publications

Baskin, C. C. and Baskin, J.M. 2007. A revision of Martin's seed classification system, with particular reference to his dwarf-seed type. Seed Sci. Res. 17: 11-20.

Baskin, C.C., J. Wurtz, Z. Liu and J.M. Baskin. 2007. A Practical Method for Breaking Physical Dormancy in Seeds of the Endemic Tibetan Plateau Shrub Sophora moorcroftiana var. moorcroftiana (Fabaceae) and Implications for Restoration. Nat. Areas J. 27: 118-123.

C.C. Baskin, J.M. Baskin and A.Yoshinaga. 2007. Imbibition and germination of seeds of Colubrina oppositifolia (Rhamnaceae), a Federal-Endangered tree species endemic to Hawaii. Nat. Areas J. 27: 25-30.

Jayasuriya, K. M. G. G., Baskin, J. M., Geneve, R. L. and C. C. Baskin. 2007. Morphology and anatomy of physical dormancy in Ipomoea lacunosa: Identification of the water gap in seeds of Convolvulaceae (Solanales). Ann. Bot. 100: 13-22.

Jayasuriya, K. M. G. G., Baskin, J. M., Geneve, R. L. and C. C. Baskin. 2007. Seed development in Ipomoea lacunosa (Convolvulaceae), with particular reference to anatomy of the water gap. Ann. Bot. 100: 459-470.

Jayasuriya, K. M. G. G., J.M. Baskin and C. C. Baskin. 2007. Cycling of sensitivity to physical dormancy-break in seeds of Ipomoea lacunosa (Convolvulaceae) and ecological significance. Ann. Bot. (doi: 10.1093/aob/mecm285)