Observations of leaf traits of Haworthia splendens and H. splendens hybrids

This blog is based on an article first published in Haworthiad , the journal of the Haworthia Society, Oct 2022. I highly recommend joining!

George Theodoris

Today I was visiting with succulent friends, and we were discussing how fun it is to create new hybrids. To me it is like an exploration of a new habitat, except it is a habitat of one’s own creation. I am encouraged by how many people have been getting into the hobby in recent years. In that spirit I will be writing more articles about my hybridization efforts. In this article I will discuss my observations of leaf traits in Haworthia splendens and progress on H. splendens hybrids from my breeding program.

Developmental and environmental factors influencing H. splendens traits

Spotting

One trait that makes H. splendens so splendid are its leaf spots. In pure H. splendens the appearance of the spots has a developmental component. Young H. splendens plants have few spots, but the concentration of spots increases after about 3.5 or 4 years. I wish I had some pictures to demonstrate this, but H. splendens seedlings are so drab looking I never bother to photograph them. The last seed batches of pure H. splendens I sowed were in 2017, and after several dull years they now look worthy of their moniker. The gene or genes that regulate spotting in H. splendens must be responsive to physiological cues that indicate the plants are aging, or perhaps the factors that cause the spots to slowly accumulate over the years. Though I have not raised as many seed batches of H. picta, I have not noticed this phenomenon in H. picta seedlings, which seem to show their spots sooner than H. splendens.

Interestingly, the developmental dependency of spotting is lost in H. splendens hybrids. Hybrids involving H. splendens may show their full spotting potential in their first year.

Color

When grown in shade the leaf spots of H. splendens are pure white. When exposed to increasing light, the leaves will produce red pigments that colour the white spots pink. I have noticed a difference between pure H. splendens and H. splendens hybrids in the amount of light required to produce these pigments. Although there is variation, pure H. splendens require more light to elicit these pigments relative to H. splendens hybrids. Fig 1 shows two pure H. splendens and two H. splendens hybrids growing side by side in one of my lower-light environments.

Leaf spots and pigments come at a price. I suspect the plants deplete precious resources to produce them. The more intensely pigmented hybrids are slower growing, more likely to stay small in stature and more temperamental to grow. In this way my breeding efforts are the opposite of most plant breeding efforts which focus on vigour and fast growth.

Hybrids with other genera

I tend to think of the white spots on H. splendens leaves as analogous to the raised white tubercles in some Haworthiopsis and Tulista. I have made hybrids between H. splendens and H. splendens hybrids with Tulista pumila “donuts” to see if I can genetically follow some of the leaf traits that distinguish the retuse Haworthia from their non-window relatives. I made two different hybrids, one using pure H. splendens as the male parent and one using one of my Scarlet Begonias hybrids (H. splendens × H. picta) as the male parent. Tulista pumila “donuts” was used as the seed parent in both cases. In the offspring from these crosses most of the progeny were pure Tulista. This is because pollination of T. pumila with Haworthia pollen stimulates self-pollination. I have observed the same phenomenon pollinating Aloe polyphylla with Haworthia pollen. But approximately 1 in 5 of the Tulista progeny made by pollinating with Haworthia pollen appeared to be true hybrids (fig 2).

Fig 2: Tulista pumila × Haworthia “Scarlet Begonias”

In these hybrids the presence of windows is recessive. None of the hybrids have features resembling the translucent leaf windows of Haworthia. The hybrids have raised white tubercles similar to, but smaller than, the Tulista parent. The leaf shape is intermediate between the two parents but closer to the Haworthia leaf shape. While these hybrids are attractive, I find them too sensitive to unsightly leaf tip dieback, at least in my conditions, to make them worthwhile as horticultural cultivars.

One of my goals in making these crosses was to produce an F2 population. F2 hybrids are made by crossing a hybrid with its siblings or a genetically similar hybrid. In the F2 generation, traits from the original plants, for example windows from the splendens parent, would reappear and it should be possible to combine different traits in novel ways. For example, I was imagining creating a plant with the Tulista leaf shape and Haworthia windows. Unfortunately, these hybrids are sterile, so this is not possible. Overcoming this barrier may be possible but will require some work and luck.

H. splendens hybrids

The first H. splendens hybrids I created were my Scarlet Begonias hybrids, starting back at the end of the 1990s. The featured picture at the very top of this blog was one of my original Scarlet Begonias selections.  It's difficult for me to fathom, but that picture was taken in 2003! It was a different world back then. For one thing I didn't need a magnifying visor to do my pollinations and my hair was less gray than it is now. The Scarlet Begonias hybrids,  named after one of my favorite Grateful Dead songs, were crosses of H. splendens and H. picta where I selected progeny for high levels of spotting and pigmentation. H. picta seems to have similar spotting genes to H. splendens and when crossed to H. splendens the progeny has varying levels of spotting. Over the years I have created new crosses and crossed the best ones together to create versions with different appearances. The best Scarlet Begonias hybrids I also crossed with other species and hybrids. Hundreds of my H. splendens hybrids were sold to China over the years and I suspect many ended up in tissue culture factories with new exotic names. Below are some of my favourite H. splendens hybrids. I have named some of these, others have not been named yet and are referred to by their hybridization number (PP#).

Haworthia “Femme Fatale”

Fig 3. This plant came out of my PP96 seed batch, sown in 2013. One parent is ((H. badia × H. truncata) × H. splendens) and the other parent is one of my Scarlet Begonias hybrids. Both parents were selected for their respective aesthetic traits. In Femme Fatale the pinks potting of H. splendens is combined with a wide pointy leaf shape influenced by genes contributed by H. truncata and H. badia. Plants from the PP96 cross were beautiful and slow growing with a tendency to remain solitary and somewhat small in size. In complex hybrids like this, there can be great variation in the appearance of the plants.

Fig 4. Another favourite, also came from this same cross.

Haworthia “Pink Galaxy”

Fig 5. This plant came from my PP169 seed batch, sown in 2016. The exact cross is ((Bev’s wonder × (H. enigma × (H. splendens × older Japanese hybrid)) crossed to one of my Scarlet Begonias hybrids. In this hybrid the typical window arrangement transforms into what looks like pink stars in the sky.

Haworthia “Pink Brackets”

Fig 6. This plant came out of my PP178 seed batch, sown in 2016. This was a cross of H. splendens to one of my Scarlet Begonias F2 hybrids. The pigmentation of this hybrid perfectly captures the pink spotting of splendens in a plant with a leaf shape that looks like curly brackets {} on the keyboard.

Haworthia PP179 selection

Fig 7. Sown in 2016. This was a cross of one of my Scarlet Begonias hybrids to my PP2 hybrids (H. splendens × older Japanese hybrid). My aesthetic is drawn to the unusual and this hybrid certainly has an unusual leaf shape and intense pigmentation.

Haworthia PP196 selection

Fig 8. Sown in 2016. This was a cross of one of my PP3 hybrids (H. splendens × (H. splendens × (H. monticola × H. pygmaea)) crossed to the hybrid “Forbidden City”. This compact hybrid captures the pink colouration of splendens in a plant with a very unusual leaf shape and morphology influenced by “Forbidden City”.

Haworthia PP322 selection

Haworthia PP376 selection

Fig 10. Sown in 2018. A cross of Scarlet Begonias to my PP86 hybrid ((Scarlet Begonias × Pink Floyd) × “Black Lady”). The leaf pigmentation of this hybrid is dark and the windows are heavily spotted and whitish pink.

Haworthia PP534 selection

Fig 11. Sown in 2020. The seed parent was my “Black Star” hybrid (Scarlet Begonias × Black Lady). Various H. splendens hybrids were used as pollen donors in this cross. This plant has pointy dark brown leaves and thick lines combined with densely spotted pink windows.