fall blooming pattern: was RE: Flowers of Crete

Jim McKenney jimmckenney@starpower.net
Fri, 04 Nov 2005 06:24:42 PST
I think this discussion of why plants bloom in the fall is revealing
something about ourselves as well as telling us something about plants.

To begin with, what is at all unusual about plants blooming in the fall
instead of the spring? The simple answer is this: because so many of us live
in severe-winter areas, and since so many of our cultural traditions are
based on the cycles as they exist in cold-winter areas, we expect the
natural world to observe those same traditions!

Rather than being unusual, I subscribe to the hypothesis that the fall
blooming pattern is the original, natural, normal one for the Mediterranean
flora, and that the spring blooming of north temperate plants is derivative,
an adaptation to the northward movement of ancestral populations from the
Mediterranean basin into higher, colder northern areas.

Autumn-blooming seems unusual to many of us simply because it does not
characterize the flora we are used to. 

The distinction made in cold-winter zones between spring and fall - very
distinct seasons in areas where winters are severe - is not so clear in a
Mediterranean climate. In a Mediterranean climate, fall is really the
beginning of the growing season for many plants, isn't it? Fall initiates
the season of moisture and temperate temperatures, both factors which
promote growth. The dry summers induce dormancy in many plants, a dormancy
comparable to the winter dormancy of plants in severe-winter zones. 

Of the Mediterranean summer and winter, isn't the Mediterranean summer the
more extreme? In other words, isn't the Mediterranean summer more hostile to
plant growth than the Mediterranean winter? The season we call fall is the
beginning of the growing season in the Mediterranean, isn't it? And notice
the north temperate bias in that word "fall": it refers to the fall of the
leaves in cold-winter areas. Many Mediterranean trees are evergreen.  

In terms of plant growth, the Mediterranean fall really corresponds more
closely to the severe-winter area spring. The Mediterranean summer really
corresponds more closely to the severe-winter area winter. 

Yes, I'm aware that many areas where bulbs are prominent in the flora offer
a double whammy: dormancy-inducing winter cold and dormancy-inducing summer

Those plants of the temperate Eurasian flora which have their ancestry in
plants from the far south almost certainly postpone the initiation of annual
growth until spring simply because northern winters would destroy soft new
growth and developing seeds.

Even a plant as tough and cold tolerant as Helleborus niger, a common
European alpine plant, will not set seed here in Maryland from autumnal or
early- and mid- winter flowers simply because we do not have snow cover. The
developing seeds freeze and die when exposed to our winter air temperatures.
Only seeds from late-winter-appearing flowers mature. The same thing
sometimes happens here with autumn blooming bulbs such as Sternbergia: in
really severe winters, the seed pods are destroyed by the winter. 

Some autumn-blooming bulbs are very well adapted to cold-winter areas. Take
Crocus speciosus for example. Although it blooms in October, its seeds do
not ripen until late April or early May - on the same schedule as those of
the late-winter blooming Crocus tommasinianus which blooms four months after
Crocus speciosus. The developing seed pods of Crocus speciosus are held
below ground until the severe winter weather is over. That option, i.e.
keeping the ovary protected underground until the weather moderates, is not
available to plants which produce their inflorescence at the tip of a long
scape. Thus, when such plants are autumn flowering, such as Lycoris, the
seeds develop rather quickly and are mature before the onset of severe
weather. The ripe seeds fall to the ground and begin to germinate
immediately, with luck under a cover of autumnal debris. 

Even those who dispute the relevance of the above for the entire or majority
Mediterranean flora will have to admit that there is a flora which grows as
if fall were spring, winter were summer, and spring were autumn. For this to
make sense, you have to remember that I am not referring to temperatures or
daylight length; I'm simply observing the seasons in which some plants grow.

So in addition to the causative factors already mentioned, I think the good
growing conditions which prevail during the fall-winter-spring period must
have had a huge influence in determining the growth schedule of the
Mediterranean flora. And to repeat, the spring-flowering pattern is likely
to be derivative.

Should any strict climatologists be reading this, my apologies for speaking
so broadly about the "Mediterranean" climate. 

Jim McKenney
Montgomery County, Maryland, USA, USDA zone 7, where Osmanthus x fortunei,
Camellia oleifera, C. sasanqua, Crocus pallasii, C. thomasii, and  C.
asumaniae have all joined the party. 

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