Sun Stress & Splash in Hoyas

What are sun stress and splash? Are they bad?

Hoya Nong Nooch displaying purple sun stress colouration

The Hoya genus is incredibly diverse in both its geographic range and morphology. Species have adapted to their environments perfectly, and in doing so have evolved ways to shift their appearance to truly thrive and camouflage in their surroundings.

A large portion of the genus have evolved the ability to change the colour of their foliage when faced with environmental stressors such as bright sun, heat and cold. This phenomenon causes foliage to shift into bright shades of red, purple and pink. Sun stressing colour changes are caused by the production of anthocyanins within the plant’s cellular system. This is an evolutionary response to growing in full/bright sun. The production of the anthocyanins changes the colour of the cells to reduce the amount of light absorbed. The result is an exquisite show of colours that we as Hoya fanatics get to enjoy. Artificial lights are an excellent way to sun stress Hoya when grown indoors. Finding the sweet spot of light is the key, otherwise foliage will burn and bleach.

Hoya wibergiae, a species that naturally develops splashing on the leaves. These splashes have then been sun stressed, creating the purple spots

Another phenomenon seen in almost every section of the Hoya genus is silver splashing. Quite often we see specimens that exhibit foliage that is entirely silver. The splashing is caused by pockets of air forming under the epidermis of the surface of the leaf. This creates the colour that we see on splashy and silver Hoya, a trait quite unique to the genus. Splashing varies from species to species however, and when carefully selected new cultivars can be created. This is seen in varieties such as Hoya carnosa ‘Grey Ghost’ and Hoya nicholosoniae ‘New Guinea Ghost’. When stable, silver foliage is a fantastic addition to any collection.

Lastly, neither splashing nor sunstressing are a bad thing. In fact, they are truly desired traits amongst Hoya collectors so enjoy the rewards of the unique traits Hoya have to offer.