RECENT ADVANCES IN CONTROL OF FLOWERING AND GROWTH HABIT OF GEOPHYTES

Geophytes can be divided in several ways as to their growth habit and flowering cycles: annual or perennial, deciduous or evergreen, synanthous or hysteranthous (leaves with or after the flowers respectively). When cultivated under growing conditions much different than their native habitat some geophytes may drastically change their growth and flowering habit.
For example, Ornithogalum thyrsoides, a deciduous perennial, when grown in the tropics becomes an evergreen which blooms constantly, does not produce bulbs and does not become dormant. Nerine sarniensis, a deciduous-hysteranthous plant, becomes an evergreen-synanthous plant when grown under constant 22°. The synanthous Crocus sativus becomes hysteranthous when the corms are held dry at constant 15°.

Seasonal thermoperiodism is the most important environmental factor controlling flowering in most bulbous plants.
For some geophytes, such as in the autumnal-flowering hysteranthus plants (e.g. Scilla autumnalis, Uriginea meritima) daily thermoperiodism is the environmental factor signaling flowering.

Some geophytes respond in addition to temperature also to photoperiod (e.g. Lilium, Triteleia laxa, Allium ampeloprasum). A special case is the hysteranthous plant Colchicum tunicatum which perceive the photoperiodic signal when the dry bulb lies well below the soil surface.

The size of the apical meristem and not the amount of the carbohydrate reserves in the bulb seems to determine its ability to form flowers.
The ethylene-promotion of flowering in Triteleia laxa is not due to enhancement of carbohydrate mobilization, but is correlated with promotion of cell division in the apical meristem and thus the size of the apex dome.

V International Symposium on Flower Bulbs

A. H. Halevy

https://doi.org/10.17660/ActaHortic.1990.266.3