Leaf Shape, Size, and Thickness

Leaf morphology describes the shape, size, thickness, width, length and fleshiness of the blade.  We use these different characteristics to tease out clues as to the particular morphology and prevalent environment where the plant evolved.All variations of the basic well considered leaf blade are adaptations to different environments. It is important to recognize and understand their implications when selecting a plant for a garden.  The morphology of the leaf will tell you a lot about how successful that choice is going to be. 

typical leaf blade we are accustomed to

No leaves

 Best place to start ! Cacti are an example of plants that lost their leaves altogether.  The photosynthetic capability was taken over by a fleshy stem.Most importantly - they do not produce a bark which is usually made of cork cells and would not be photosynthetic.  Instead, the stems are made of epidermal cells - green, live and full of chlorophyll.  Hence why so many cactus tend to be short, stout and very rarely large. Some however, like saguaro, produce an internal wood structure in the center  which keeps them upright! 

typical cactus stem with no leaves nor bark !

Estivation leaves

 These are an adaptation to seasonal or infrequent rains. The leaves show up only after the rainy season begins.  Some succulents (not all!) are an example of this.  A common indoor plant Euphorbia also has estivation leaves which defoliate in the dry season.  Both are indications of adaptations to hot, dry environments with infrequent rains. 

Euphorbia trigona

Fleshy leaves

 These are basically water storage adaptations. Case in point: Succulents. These evolved in environments of infrequent rains. Their root systems tend to be very long horizontally.  This helps them to maximize the area where they can obtain water when it does rain. 

a collection of succulents

Savannah leaves

 Areas of infrequently rain, but more so than deserts - we call savannahs.  Plants here tend to have long strap like leaves that are arranged centrally and grow outward at 45* angles from the center.  These function to channel rainwater towards the center of the plant so it runs directly down the trunk and onto the roots. Samples include Agave and Dracaena.  

Shade leaves

 Large blades evolved in shadier environments, as did whole leaves. They grew thinner, wider and longer. 

Hosta

Sun leaves

 Small leaves is an indication of a full sun environment. Boxwood is a good example.

Boxwood leaf (Buxus genus)

Compound leaves

 Originally all plants had a single blade.  But as a response to predation by insects, particularly the Lepidoptera (caterpillars) they developed compounding.Compounding helps in as much as the way caterpillars eat.  Many tend to eat in an arching fashion moving back and forth until they consume the entire leaf.  This keeps them on the leaf without moving around much.  But they have another particularity - many times they drop off a leaf once they have consumed it.  Compounding the leaf keeps the damage to a minimum.

typical compound leaf

Roll up leaves

 Grass leaves are long and narrow, evolving in areas of full sun with infrequent rains.  Their basic long thin shape keep water loss to a minimum.Some further evolved and have an additional adaptation - to roll up as a response to dry conditions. In fact there are specialized cells at the base of these leaves called bulliform cells which have a fan shape.  When there is insufficient water, they collapse on themselves and help the leaf roll up like a cigar ! 

typical grass leaves

Cylindrical leaves

 This particular shape evolved to reduce the overall surface area.  Here leaves adapted to dry conditions with low rainfall and lots of wind.  A mountain top pine tree is a great example. 

mountain top Bosnian pine

Small thick and hard leaves

 These leaves are from plants that evolved in environments that were dry and hot.  Juniper is a good example. 

Juniper torulosa

Paper thin leaves

 Ferns in general evolved in moist or humid environments with frequent rains in full sun. This is clearly demonstrated by their paper thin leaves with little to no wax on their surfaces.The hairs and scales on their leaves are an adaptation to defending the uncurling new leaf from browsing animals. Some later evolved to adapt to partial sun or shade conditions. 

Japanese painted fern

Our Landscape Design Team uses these criteria when selecting plants for the long term survivability of your garden.

Call us - let's talk leaves !

PLANT SPECIALISTSGREENING NEW YORK FOR OVER 53 YEARS !

   Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBAAll photographs used with permission @SHUTTERSTOCK