Similar to any other plants, the leaves of Hoyas are referred to as the “plant factories” because it is in the leaves where plants make its food (thru the process called photosynthesis). It is also where water evaporates from the plant and the exchange of CO2 and oxygen takes place. Usually the leaves are your health indicator of whether your Hoyas are overwatered or underwatered and whether your Hoyas are happy or sad.
Parts of a hoya leaf
Apex - the upper ~25% of the lamina Base - the lower ~25% of the lamina Lamina (blade) - the expanded, flat part of a leaf or leaflet Margin - the edge of the lamina Petiole - the stalk of the leaf Primary vein - the widest vein of the leaf and any others of like width and/or course. Primaries usually originate at or just above the petiole. Secondary vein- the next narrower class of veins after the primary, originating from the primary or primaries. Tertiary vein - the next narrower class of veins after the secondaries, originating from the secondaries or primaries (this is not shown in the picture but they are the smaller ones)
CHARACTERISTICS OF HOYA LEAVES
Hoya leaves are simple. Simple means consisting of single lamina or blade. However, Hoya leaves differ greatly in size, texture, colour and venation. Hoya leaves can vary from very thin ( Hoya polynuera) to semi-succulent ( Hoya carnosa) to very succulent (Hoya pachyclada and Hoya kerii).
In size, Hoya leaves range from as small as 5 mm in length and 2 to 4 mm in width (Hoya engleriana ) to as large as 25 cm by 35 cm. (Hoya latifolia ).
Hoya coriacea Blume, has been reported to have leaves as long as two feet in length. There are hoyas with almost perfectly round leaves (Hoya serpens) and others with linear leaves (Hoya linearis and Hoya teretifolia, Hoya acicularis.).
One popular species, Hoya shepherdii has leaves that resemble string beans hanging in bunches from their stalks.
Hoya linearis is covered with fine downy hair and resembles masses of Spanish Moss hanging from trees in its native habitat. There is also the Hoya retusa with elongated, flat and narrow leaves that grow in clusters, with a wispy, almost succulent look to them.
Some Hoya leaves are smooth and shiny; some are covered with hairs. Some Hoya leaves appear to be veinless while others have very conspicuous veins of a lighter or darker colour than the rest of the leaves as in H. cinnamomifolia.
Some have leaves that are mottled with speckles of silvery white or pink silver (Hoya carnosa , Hoya pubicalyx, Hoya caudata).
Some hoyas have leaves that are thin and translucent (Hoya coriacea Blume); some are so thick and succulent that they look more like crassulas than hoyas (Hoya australis ssp. rupicola, oramicola and saniae from Australia and Hoya pachyclada from Thailand).
One of the most succulent, Hoya kerrii has obcordate (inverse heart-shaped) leaves, with the cleft away from the stem.
HOYAS WITH STRANGE LOOKING LEAVES
Hoya leaves are produced in opposite pairs at stem nodes, although sometimes, hoyas produced one leaf per node. Hoya imbricata is a very unusual hoya because it never develops more than one leaf per node. And then there is a very strange Hoya called Hoya spartioides because this hoya is made up entirely of peduncles with leaves almost never making an appearance, and if they do, they are very short lived. Another very interesting kind of Hoya is the Hoya darwinii. This hoya produces leaf shelters or hiding places for ants and they live in symbiosis.
The variation in the leaves is often due to the environment of the hoyas. Thinner, darker, larger leaves often mean that the hoya is more accustomed to shadier, wet environments (e.g., Hoya multiflora), whereas thick, succulent, lighter-colored leaves likely mean the Hoya requires fuller sun and can withstand some level of drought (e.g., Hoya diversifolia). Hoya species in dry environment often have more succulent leaves to be able to store water or at least not loose water too quickly.
My observation: – hoyas with thinner and smaller leaves like my Hoya polynuera and Hoya bella does not retain water for too long (the water evaporates quickly), hence I water them more frequent than my hoyas with semi-succulent leaves like my Hoya carnosa. And then I water my Hoya kerii, because it has the most succulent type leaves, less frequent than the Hoya carnosa.
OTHER INFORMATION ABOUT HOYA LEAVES
These information can be used as guidelines in putting labels or names to your hoyas. Hoya densifolia and hoya cumingiana, two hoyas that look very similar, were distinguished based on the shape of their laminas (Hoya densifolia is ovate while hoya cumingiana is obovate).
Some hoyas were also named based on their laminar shape like the following: Linear shape – Hoya linearis Lanceolate (shaped like a lance head) – Hoya lanceolate aka Hoya bella Elliptical – Hoya elliptica Undulate – Hoya undulata Acicular – Hoya acicularis Obovate – Hoya obovata
LAMINAR OR BLADE SHAPES OF HOYAS
THE SIZE OF THE LAMINA
The laminar size is determined by measuring the area of the leaf. An approximation can be made by measuring the length and width of the leaf in millimeters and multiplying the length x width x 2/3. If the answer is < 25, then the blade class is called leptophyll, from 25-225 it is called nanophyll and it goes on : 225 - 2,025 - Microphyll 2,026 - 4,500 - notophyll 4,501 - 18,225 - mesophyll 18,226 - 164,025 - macrophyll >164,025 - megaphyll
Credits to Dr. Inocencio Buot, Jr. and his team who organized the Hoya training in University of the Philippines and the speakers/lecturers Dr. Fernando Aurige, Ms. Marj Delos Angeles and Ms. Jeanette Mara Tan. And to those people who posted pictures of their interesting hoyas in the internet that i used in this post