Hoya Foliage - Their Leaves
A Pictorial Guide
Hoya leaves are highly variable in size, shape, thickness, texture and venation. They may be glabrous or hairy. The leaf is made up of a petiole and a blade (see labeling on previous page). The blade may have hairs on both surfaces or on only one surface. These hairs are simple or uniseriate. They are thin-walled, very fine, and usually white and vary in length and dispersion. The texture varies from thin e.g. Hoya microphylla, to very thick and succulent e.g. Hoya australis ssp. rupicola, depending on the species and also its habitat. There is usually one or a group of nectariferous glands at the junction of the petiole with the leaf blade.
The leaf surface is covered with a relatively thick wax layer (cuticle) above the single celled epidermis. Below the epidermal layer are palisade cells and below this the spongy parenchyma, throughout which is the scattered vein system. Below then the lower epidermis. In Hoya species the mesophyll varies from undifferentiated to strongly differentiated. There is usually a lot of sclerenchymatous mesophyll fibers, like a mat of tangled spider webs. This later also varies in its presence and thickness among the different species.
It should be mentioned that leaf size shape are the most variable structure of a hoya plant due to environmental factors of light, nutrition, genetics and other factors even in the wild and more so under domestication. Leaves of hoya may have various distinctive markings on the upper leaf surface. This can be spotting, streaks and blotching. This arises from irregular concentrations of chromoplasts (colored cell inclusions) in cells immediately below the upper leaf surface.
- Part 1, pg 1~21 .pdf document
- Part 2, pg 22~168 .pdf document
- Part 3, pg 1~37 .pdf document
- Part 4, pg 1~61 .pdf document
- Part 5, pg 81~99 .pdf document
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