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The case of the spiny eggplants

You've heard of prickly pears. But are you aware of their equally intriguing and just as needly relatives, the spiny solanums? The relationship is not botanical, mind you - those pears belong in cactaceae, whereas the topic of this page concerns a few species in solanaceae. But they do share some other characteristics besides the need to wear gloves to handle them: attractive, and sometimes edible, fruit, and a bit of an oddity in the garden. Sound interesting? Read on — I'll describe the six species I've grown on the page below.

My first experience with this botanical genre came early in my gardening career. I had just taken up seed-starting, and had yet to discover the wonderful world of online seed trading. Instead, I collected seed catalogs, and placed orders with quite a number of suppliers. An early favorite was the catalog of J.L. Hudson, Seedsman - both for the reasonable prices and the wild variety of interestingly described plants. Among the many curiosities I ordered were balsam pears, hairy-leaved chiles, and bundleflowers, some of which still inhabit our garden. But the one I remember best was Solanum atropurpureum, whose description included a quote from a botanist proclaiming the majesty of this ferocious plant, ending in I call it 'Malevolence'. I can no longer find the full quote (let me know if you have an old catalog containing the blurb!), but 'Malevolence' has always stuck with me; I continue to call these plants by that name.

S. atropurpureum sure was an oddity. Already as a seedling, it had purple stems, and was covered in sharp thorns - not just along the stems, but along the leaves too. That year I shared many extra seedlings with a fellow gardener. I made sure he left with a couple of Malevolence seedlings, which seemed to intrigue him as much as me. But when I asked after the plants a few weeks later, he confessed they had not passed his wife's approval, and had not been admitted into their family garden. My dear wife knows better than to interfere directly with my botanical experiments, so our plants grew and prospered. And so began my interest in this little corner of the Solanum genus.

Since then I've sought out several others; each is quite distinct, and described with photos below. All of them are in the subgenus Leptostemonum of genus Solanum (which also houses the common eggplant), but their paths diverge from there: they belong to different sections of the subgenus. If you know of any additional ones I should try, please let me know.

Solanum atropurpureum: stately malevolence

Habit. This is the tallest of the four, growing sturdily to at least five foot tall when it's happy. It's big around too, so that a few plants make quite the impenetrable thicket. The species gets its name from the deep purple, almost black, coloration of the stems and thorns.

Thorns stand in amazingly dense formation along the main stalks. They also run along the leaf stalks (petioles), the flower/fruit stalks (peduncles), and along both the tops and the bottoms of the main ribs of the leaves. They stop short of the fruit itself, which can be picked without too much danger of puncturing fingers.

Flowers start appearing in the heat of summer, in mostly downward-facing clusters. The recurved petals are creamy white, while the bundle of stamens is a stronger yellow. Not particularly showy, but nice enough up close.

The fruit competes with the dark-shiny thorns for the distinction of 'most noteworthy aspect'. The plants set an abundance of it, about the size of common marbles. They start off striped in two tones of green, then color a rich yellow by early fall.

Solanum virginianum: Christmas tree eggplant

The classification of this one is confused; I received this as (seed of) S. surrattense, but according to GRIN the correct taxon is S. virginianum, another synonym being S. xanthocarpum. All three names are found in online references to similar plants, sometimes with photos and descriptions that don't quite match the plants we've grown under this name. If you know the details, please feel free to set me straight! Common names include Surrattense nightshade and Kanta Kari; I assume the latter is the name used in India, its native country. I've found it used mostly in an herbal context. Although I can't vouch for the medicinal benefits of the fruit though, it supposedly has mild purgative as well as antibacterial properties. In Indian medicine it is even used to combat balding of the scalp. Your mileage may vary.

Habit. Although in proper climates this grows to be a shrub, when grown as annuals they are quite a bit shorter in stature than atropurpureum, ours haven't grown taller than two to three feet.

Its light green thorns aren't as eye-catching as some of the others, but just as sharp. Most parts of the plant, including leaves and fruit bracts, are prickled.

Leaves are mid-green, softly hairy (that is, where they are not prickly), with irregular (but not particularly lobed) margins.

Flowers arrive in early summer. They are white and face downward - not much of a show.

It's the fruit that really defines this plant. They are squat, the largest about the size of a chestnut. These too start out stripey-green, and progress to yellow. But they don't stop there: after yellow comes orange. The fruits ripen at different times, so that by late summer all colors are represented. It's even more interesting-looking after a freeze has killed off the foliage, the fruit still dangling colorfully from the darkened branches.

Solanum pyracanthos: prickly orange

The species name of this plant, hailing from Madagascar, is Greek for fire-thorn; I've also seen it called porcupine tomato. Both names are appropriate for this startling plant!

Habit. Not quite as tall and a bit more freeform than atropurpureum, this is still a substantial plant. It does well when provided consistent moisture, in which case it can grow to four foot tall in one season.

There's no doubt the the thorns steal the show on this one. They are long and feasome, colored orange to yellow, and clearly meant to protect all parts of the plant: all stems are covered in varying density; the leaves have spines not just along the midrib but also along several other nerves; and for those who would dare pick the fruit, the plant sends fierce prickles downward along the fruit bracts.

The soft hairs on the leaves and stems gives them a dull or silvery green appearance, depending on how the light hits them. The leaves are long, and lobed in a gentle zig-zag.

Attractive purple flowers with prominent yellow anthers keep coming all summer. They look like those of the common eggplant, with papery-crinkly fused petals; look at the backside of the corolla to see a silvery star.

Fruit starts out inconspicuous, and stays fairly small - the size of a large blueberry. It doesn't ripen until early fall, when it eventually turns yellowish orange.

Solanum sisymbriifolium: vicious pricklefruit

This species, native to South America, is generally classified as a weed. I would have to agree that it's the least gardenworthy of the ones on this page, but I'm still glad I've grown it. Its common names include sticky nightshade and litchi tomato.

Habit. Like real tomatoes, this plant can't decide whether it wants to grow up or sprawl. When young, the plants are well enough contained, but as the season progresses the stalks grow more wildly, posing a scratch hazard to passers-by.
Its thorns aren't ornamental. They are green and not terribly long (though still plenty sharp), occuring mostly along the stems, with some wayward prickles along the leaves. The only thorns that are visually prominent are the ones protecting the fruit.
The leaves are architectural, and quite handsome in strongly growing plants. They are deeply divided along their considerable length, with wavy serrations along each of the divisions. Leaf surfaces are hairy and prominently veined, contributing to an attractive three-dimensional look.
The flowers are actually quite nice: varying in color from powder blue to white, with bold yellow anthers, they are held above the leaves and are large enough to make a statement.
It is fascinating to watch the fruit develop. Soon after the flowers fade, viciously thorny husks develop from the bracts to protect the developing fruit. They remind me of medieval weapons. After some time the casings start peeling away, to expose yellow berries. Finally, as the bracts shrivel up, the berries turn shiny bright red - looking indeed much like a small tomato. They reportedly have culinary uses similar to tomatoes, but I'm not sure I'd want to harvest them in large quantities. Even just harvesting enough for seed, my fingers didn't appreciate the encounters with the shriveled husks; the thorns seem to only get sharper as they dry.

Solanum quitoense: naranjilla's velvet deception

Another South American species, this one will grow into a tree given the right conditions. The plant and its fruit are known as naranjilla.

Habit. The most striking feature about this plant are its large leaves, which announce 'I'm Tropical' with a sense for drama. Through the years, I've made three attempts to grow it. The first two times I was pleased with its verdant velvety leaves, which stayed close to the ground – I thought that was all I was about to get from this perennial species in a single year's growth, but my recent attempt proved me wrong. For reasons unknown to me, my two plants took off vertically, making many more leaves on sturdy stalks. By late summer, they overwhelmed the rose in front of which I had placed the naranjillas. I guess this was their Dr. Jekyll year.
Even more interesting is its attitude towards thorns. I don't recall seeing any during either of my first attempts; the more recent lofty duo mixes it up: one is entirely without thorns, the other has them in all the regular places: on the top and bottom surfaces of leaves (most prominently along the main veins), and along the stem. In all, the prickles are not important ornamentally, but I'm intrigued about the genetic reasons behind my observations (all plants were grown from the same seed lot). visually prominent are the ones protecting the fruit.
Did I mention that the leaves are large and velvety? Do not pet the naranjilla - it may have hidden prickles. On young plants, the veins that traverse them are a lighter shade of green; older plants feature pink veins. The leaf margins are attractively scalloped.
Flowers arrived late in the year, and only in my most recent cultivation effort. Fuzzy purple buds appeared close to central stem, mostly obscured by the leaves above. A few weeks later, they opened to thick-petaled white flowers, which contrast with the purple bracts. Not highly ornamental, but worth bending over for a closer look.
A few weeks after the flowers appear, the fruit develops. I hope to have more information soon – right now, I just have small greenish starts. Ours may never ripen, but if they do, they reportedly make a nice fruit juice.

Solanum rostratum: bane of Texan buffalos?

This one hails from less far-flung regions: it is native to the U.S. plains states, where it can be a troublesome weed of pasture land. Its common name is buffalo bur. A friendly gardener from Texas found this page, and sent me some seed so I could try an additional spiny solanum. Even given its reputation as a pest, I had to attempt it at least once – but one season of growing it in less than optimal conditions won't allow me to do it as much justice as the other species described here.

Habit. Not so tropical. Given the location I provided (dry, not too fertile – why pamper a weed?) my plant probably didn't reach its full potential. It will grow one to two feet tall, but mine stayed at the lower end of that range, with a scraggly habit. During much of late spring and early summer it was barely visible, and feasted on by flea beetles. It did come into its own in late summer, but by then the drought conditions had driven me from the garden, so I didn't pay as much attention.
The thorns on this one are of the functional rather than ornamental variety. The stems are lined with little sharp prickles, some light, some dark in color. I didn't notice thorns on the leaves.
If the overall habit were more attractive, the leaves of this species could be quite an asset. I liked the irregular, squiggly margins on the bluish green composite leaves.
Flowers appeared in September. The bright yellow fused petals have a crinkly texture and are more substantial than those of most other species described here. The prominent stamens are also yellow. Overall, quite attractive.
Several weeks later, I noticed the fruiting bodies. Predictably, they were covered in impressive thorns. I was pleased that they got to this stage, but neglected to observe their further development. So I don't have photos of the actual fruit to share.

Garden use and cultivation

I've not experimented sufficiently with these plants to know how they respond to different garden conditions. It's safe to say they all appreciate a healthy dose of sunshine, and reasonably fertile soil. Some are thirstier than others - S. sisymbriifolium and S. atropurpureum have thrived in fairly dry conditions, where the others would have struggled.

So how to use these striking plants in the garden? My dear wife might advise "Just don't do it", but of course that's not an option for the curious gardener. My advice is to keep in mind that these plants grow to a substantial size, and place them accordingly - far enough back in the border that the arching stems won't reach to grab hold of skin and clothing of passers-by, but not so far back as to hide their distinguishing features. This takes some experimentation - last season, the S. pyracanthos I planted close to a newly planted rose wound up overpowering its equally thorny neighbor, as well as the plantings in Lily's girl-garden to the other side. I guess the fertile soil I provided for the rose worked wonders on the solanum as well!

Flea beetles and false potato beetles both feast on S. pyracanthos and S. rostratum, just as they do on edible eggplants. For much of the year, the leaves are dotted with small holes, which does detract from the plant's appearance. For some reason, the pests are less attracted to the other species.

The first four species above are more cold-tolerant than the common edible eggplant (S. melongena); they still stand proud after a few autumn frosts into the high 20s, before they finally give up when the temperatures dip even lower. I tried once to overwinter S. quitoense indoors, but it didn't work out – that's par for the course for me, I'm no good at getting tender plants through winter.

Propagation

The fruit of each of these solanums are chock full of seeds, so that just a few berries suffice to get a good seed harvest. They ripen late, well into autumn in our climate. Luckily, I've found that the seeds are still viable even after the berries have been subjected to hard freezes - so I usually wait till November to harvest.

Germination is easy. All species sprout fairly quickly at temperatures slightly above room temperature. They proceed to grow strongly, so don't start them too early; I usually wait till late March, so that I can start hardening the seedlings off in late April, and set the plants into the garden in May.

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