Why do Needled Evergreens have that leaf shape ?
Pine branch tip showing needle - like leaves
BASICS
Needled evergreens evolved as a group soon after the adaptation to land occurred in plants. They were one of the first land plants to become tall trees.They evolved in full sun environments due to their competitive advantage of height over all other plants at the time - mainly mosses and pteridophytes. The size and shape of the leaf – long thin leaves was an adaptation to wind.
the typical place where Pinus evolved - a ledge on a mountain top
Their leaves evolved in full sun - thin, hard, evergreen - and thus poorly adapted to anything other than that full sun environment. That is why they do not do well in shade - their leaves are unable to adapt. Shade plants evolved thinner and wider leaves.
cross section of Pinus leave showing its cylindrical shape
They also evolved volatile aromatics in their pine resin and oil - an adaptation to warding off predators from eating them. The resins exuded freely from leaves, stems, and roots.
pine resin
Needled evergreens did continue to evolve even after the arrival of the broad leaf deciduous and evergreen plants millions of years later. One adaptation was the formation of white wax on the cuticle, thus forming a whitish or blue whitish tinge to the leaves in environments that were not only sunny, but dry as well.
white wax on leaf surface - an adaptation to dry environments.
Needled evergreens that evolved in hot dry environments never developed hairs on their surfaces, since their leaves were already so hard and impermeable to transpiration loss. The implication from their morphology is that as a group they prefer windy and sunny environments with infrequent rains.
Bosnian pine on dry windy mountain top
A look alike but NOT !
Taxus also evolved “no wax” on their leaf surfaces. These became shiny green and smooth. These were also from sunny environments - but cooler and wetter as well. Notice also that Taxus has the beginning signs of an adaptation to a somewhat rainy environment seen in its sharp pointed leaf tip.
Taxus baccata
Taxus is not related to Pine, nor does it produce oils or resin. But it does adapt somewhat to a shady environment and as such is the "go to" for an evergreen in low light.
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Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBAAll photographs used with permission from @SHUTTERSTOCK