Monday, January 16, 2017

Dendrobium kingianum: the pink rock orchid

Dendrobium kingianum
Dendrobium kingianum is an Australian species popular among orchid growers. I love the delicate coloring of these flowers, and hybridizers must have too; Dendrobium kingianum has provided either the pollen or the seed to 158 registered crosses!

In its natural environment, Dendrobium kingianum usually grows in or around rocks (as a lithophyte), across much of eastern Australia, covering many habitats and weather patterns. I suspect that this variety of natural growth conditions is why Dendrobium kingianum is reputedly easy to grow in culture.
Closeup of Dendrobium kingianum flowers
Dendrobium kingianum flowers are about 1 inch across.  Lavender varieties like the one I photographed at the Bronx Botanical Garden are the most common.  However, flowers can range from white to deep purple. Australian Native Plants Society has some beautiful photos of purple and white varieties.

Dendrobium kingianum culture notes. (Massachusetts Orchid Society)

Saturday, January 7, 2017

What causes a phalaenopsis to grow a keiki?

Phalaenopsis keikis: Noid Phal keiki on left, Phal Gold Tris keiki on right
Happy 2017 everyone! December/January tend to be a colorful time for orchids in my terrarium.  The shorter, colder days of September provide the perfect signal to induce my Phals to spike.  The flower spikes generally develop over the next two months, and come into full bloom around the turn of the new year.

However, this year, some of my spikes started growing aerial plantlets (or keikis) in addition to flower buds.  The keiki on my noid phal looks like a leaf growing off the side of a new flower spike.  Meanwhile, Phal Gold Tris produced a tiny plantlet at the tip of an old spike that bloomed over the Summer.

I have written about growing and separating phalaenopsis keikis in the past, but this time I was curious about what caused my orchids to produce keikis in the first place.

What causes a phalaenopsis to grow a keiki?

The internet has many claims about what causes an orchid to make a keiki, but offers little evidence in support.  And even in the research literature, I struggled to find a definitive answer.

So what do we know about Phalaenopsis keikis?  I found a common claim that if a phalaenopsis with a new spike (<4 inches) is exposed to temperatures above 28C (82F), then the spike will develop keikis instead of flower buds.  

See examples:
if a plant with a young inflorescence (less than 4 inches or 10 cm) is subsequently grown at 82 F (28 C) or higher, a spike can form a vegetative air plantlet known as a “keiki” instead of flower buds, buds may abort or both. (Phals article from  
"if a plant with an inflorescence <10cm is subsequently grown at 28C or higher for extended periods, a spike can form a vegetative air plantlet referred to as a "keiki" instead of flower buds, buds may abort, or the stem may elongate indefinitely without open flowers [Sakanishi et. al 1980]"  (Roberto G. Lopez and Erik S. Runkle, 2005)
However, when I tried to find the original source for this claim, its evidence is weak.  Sakanishi et al is a 1980 paper describing the Effect of Temperature on Growth and Flowering of Phalaenopsis amabilis. However, this paper never actually reported any keikis!

In fact, the authors found that high temperatures caused flower spikes to abort growth and flowering.
With the object of determining the effect of high temperature treatment started from the different stages of stalk elongation, 12 plants in the greenhouse were shifted to minimum 28C at each time when flower stalks reached a length of 5, 10, 21-30, and 41-50 cm.  The high temperature from the 5cm stage caused the abortion of florets or the stunted growth of the flower stalks. After the stalks elongated more than 10cm, every stalk normally developed into flower even at the high temperature.
 In the closing remarks, the paper references an even older study on Phalaenopsis schilleriana, which makes the claim about keikis being triggered by temperature.
At ...(maximum temperature 29-34C; minimum temperature 24-25C), [Phalaenopsis schilleriana]  adult plants develop a stalk, which remains vegetative and develops an adventive plant.           (De Vries JT, 1953)
This paper "On the flowering of Phalaenopsis schilleriana" dates back to 1953, and is not available online.  Thus we only have a second-hand description of its findings from the Sakanishi paper.  However, it appears to be the sole parent of all the claims regarding temperature control inducing keiki formation.

What does keiki paste do?

A number of companies sell a product called "keiki paste" which when applied to a dormant node on a flower spike can help induce growth of a keiki.  The active ingredient of keiki paste is a chemical called BAP, or benzyl adenine.  BAP is a synthetic plant growth hormone.  It stimulates activity from flower spikes, and can produce either flowers or keikis depending on environmental conditions.

Which still does not answer our original question about what conditions make a Phalaenopsis develop a keiki instead of flowers.

The final verdict?

I don't think we actually really know the answer to this question. 

Orchid research is not particularly interested in this question. Commercial growers optimize conditions to produce flowers, not keikis.  And keikis are an inefficient way to reproduce orchids on a commercial scale, leaving little incentive to study keikis when there are important questions to be worked out in meristem cloning and in vitro seed germination techniques. 

If anyone reading this has come across a different claim about phalaenopsis keikis, I'd be happy to look into whether it has a scientific backing.  However, in the meantime, I don't think we know what cocktail of light/temperature/water/nutrients is the Goldilocks recipe to trigger keiki growth.