Hillia triflora and the bird pollination syndrome

Hillia triflora flowers in the typical cluster of three at the end of a branch

Hillia triflora is a somewhat obscure epiphytic shrub in the coffee family, Rubiaceae. I didn’t know it existed until I ran across a small cutting for sale on eBay a few years ago, and after a quick google search, I made certain that I would be the high bidder when the auction ended. It’s a hummingbird-pollinated plant, and as I have noted before, this gardener is attracted to the same floral features that attract hummingbirds.

H. triflora comes from central America, with specimens collected from southern Mexico to Colombia, and although it usually grows at higher elevations, plants have been found at only 100 m above sea level in Costa Rica [1]. As might be expected from this wide geographical and altitudinal range, the plant seems to be quite tolerant of both summer heat outdoors and cool winter nights in the greenhouse. There are two subspecies with overlapping range, H. triflora subsp. triflora, and H. triflora subsp. pittieri; judging by the equally sized leaves on flowering shoots and narrow, uninflated flowers, my plant belongs to the nominate subspecies [1].

The growth habit of this plant is very interesting. It forms an open shrub with flexible, infrequently branched stems bearing opposite, semi-succulent leaves. Each stem terminates with a protective sheath. Over the course of a couple of months, the sheath slowly swells and eventually splits, revealing that it was formed by a pair of bracts tightly pressed together. Emerging from the sheath is either a new stem segment with a pair of leaves and new sheath, or a cluster of (usually three) flower buds. At the base of the flower buds is one or more new sheaths, so the stem sometimes branches after flowering.

Sheath at the end of a branch. At this stage in its development, it is difficult to see that it is composed of two bracts.

The roots of H. triflora are fibrous, without obvious adaptations to epiphytic life, and plants in habitat are occasionally found growing terrestrially in leaf mould or rotting wood [1]. Consequently, I added some coarse peat to the mix of orchiata bark and perlite in which I potted my plant. I water when the mix is almost dry, and so far the plant seems happy. It grows with my vireyas under shade cloth in summer and goes back in the greenhouse when temperatures drop below 50 F (10 C) at night.

The flowers of H. triflora are very similar to those of the unrelated coral honeysuckle, Lonicera sempervirens (Caprifoliaceae), that grows wild in the woods around my house–it’s a remarkable case of convergent evolution driven by birds. I would guess that the hummingbird responsible for pollinating H. triflora is roughly the same size as the ruby-throated hummingbirds (Archilochus colubris) which pollinate L. sempervirens. I suppose it is even possible that A. colubris is a pollinator of H. triflora, given that the birds over-winter in central America and H. triflora has flowers in November/December as well as March-May [1].

Lonicera sempervirens flowering at the edge of our woods today

Lonicera sempervirens (top) and Hillia triflora (bottom)

I have previously featured a variety of hummingbird pollinated flowers on this blog, both native plants (Aquilegia canadensis, Aesculus pavia, Lobelia cardinalis, Lonicera sempervirens, Spigelia marilandica, Silene virginica) and tropicals (Juanulloa mexicana, Macleania sp. aff. smithiana, Macleania pentaptera, Ceratostema glans, Cavendishia capitulata, Bouvardia ternifolia, Bessera elegans, Behria tenuifolia, Columnea microcalyx, Columnea crassifolia). These flowers share obvious characteristics: bright red/orange/magenta color, tubular (or sometimes bell-like) shape, lack of fragrance, and copious nectar. The same features are seen in plants from Africa, Asia, and Australasia where there are no hummingbirds. In those locations, sunbirds (Nectariniidae) and honeyeaters (Meliphagidae) fill much the same ecological niche. However, because sunbirds and honeyeaters are less likely to hover than hummingbirds, bird-pollinated flowers in the old world are usually not pendant and are often attached to a stout inflorescence that allows the birds to perch (see, for example, Cyrtanthus obliquus).

Dermatobotrys saundersii is an epiphytic shrublet from South Africa that is likely pollinated by sunbirds. It is easy to grow from seed but seems not to like hot North Carolina summers. I have been unable to keep plants going for more than a couple of years.

The flowers of Dendrobium chrysopterum from New Guinea bear all the hallmarks of bird pollination. Like similar Dendrobium orchids, they may be visited by honeyeaters.

Reference

1. Taylor, CM (1989). A revision of Hillia subg. Ravnia (Rubiaceae: Cinchonioideae). Selbyana 11: 26-34.

Six on Saturday #74 (April 22, 2023)

Happy Earth Day! This would be an obvious day for working in the garden, but unfortunately we will have thunderstorms rolling through for most of the day (though luckily the potential for tornadoes seems to be southeast of our location). Here are a few pictures taken this morning before the rain, rounded out with a couple taken earlier this week.

1. Paeonia ‘America’

I planted this herbaceous peony about three years ago. It produced its first buds last year, but they all froze and aborted. This year, two buds survived, and I finally have the first flower. Each day, the flower starts to open after I leave for work and closes before I get home, so it was tricky to get a photo. The flower is already closing in this picture, and I only saw it partially open because I left work early to catch eldest offspring’s last high school tennis match.

2. Paeonia obovata (Japanese woodland peony)

This peony does well the shade under a dogwood, where it grows among trilliums and Calanthe orchids. The white-flowered form sometimes goes by Paeonia japonica, but Kew lists that name as a synonum of P. obovata.

3. Calycanthus floridus (eastern sweetshrub, Carolina allspice)

This native woodland shrub is famed for its fragrance, which is often compared to fresh strawberries. My plant smells more like overripe fruit–not horrible, but not something I’d seek out. If buying one to grow close to the house, it’s probably best to shop for plants in flower and give them a sniff test before laying down your money.

4. Actias luna (luna moth)

Luna moths only live for a few days after completing metamorphosis, and this one was at the end of its lifespan. It could no longer fly, and was fluttering weakly across the lawn this morning.

5. Quercus phellos (willow oak) growing on Juniperus virginiana (eastern red cedar)

Not in my garden, but local, are two of my favorite individual trees. The pale green leaves are a small willow oak which is growing epiphytically on a red cedar. The oak must have grown from an acorn that fell or was deposited by a squirrel into a crack in the trunk of a red cedar. Enough water and organic debris sifts down to keep the oak alive, and I have been watching it grow slowly for almost a decade. Each spring, it’s always encouraging to see that the little oak has survived another year.

6. Allium schoenoprasum (chives)

Garlic chives, Allium tuberosum, seem to be more vigorous in this climate, but this little clump of chives is doing fairly well. It’s in a raised bed shared with walking onions and garlic chives, which are permanent residents of the bed, and two varieties of garlic (softneck and hardneck), which will be harvested in June.

Jim at Garden Ruminations is the host of Six on Saturday. Head over there to see his Six for this week and find links to the blogs of other participants.

Six on Saturday #73 (April 1, 2023)

It’s been a while since I have had the time to put together a Six on Saturday post. Spring is well underway here in the North Carolina piedmont. The early Narcissus have long finished flowering, and only late-flowering clones like ‘Thalia’ and ‘Golden Bells’ are still in bloom. Azaleas are just getting started. The native pinxter flower, Rhododendron periclymenoides is in full bloom, and the buds are opening on Florida flame azalea (R. austrinum). My hardy Calanthe and Bletilla orchids were hit hard by a freeze after a prolonged frost-free spell, and many of their new growths were turned to mush. It remains to be seen how many flowers they’ll make this year.

Here are six plants from the greenhouse and garden that I haven’t featured before.

1. Rhododendron ‘Aravir’

‘Aravir’ is another of the modern vireya (tropical Rhododendron) hybrids. Its parentage is R. konori x (‘Pink Delight’ x jasminiflorum), which explains its similarity to the Victorian ‘Princess Alexandra’ (R. ‘Princess Royal’ x jasminiflorum). The parentage of ‘Pink Delight’ is unknown, but it was an old Veitch hybrid, so probably similar to ‘Princess Royal’. I got this plant as an unrooted cutting about 2 1/2 years ago, and this is the first time I have seen it flower. I am currently experiencing (hopefully temporary) post-COVID anosmia, so I can’t say much about its fragrance. I can barely detect a scent, which probably means that it is very strongly scented. Like all vireyas, this plant is not frost-hardy. I grow it in the greenhouse in winter and outdoors under shade cloth in summer.

This is one of a group of vireya hybrids with names drawn from the Chronicles of Narnia. ‘Aravir’ refers to the Narnian morning star.

2. Columnea crassifolia

This beautiful epiphytic gesneriad is from Guatemala, so it is a greenhouse plant. The large hummingbird-pollinated flowers are similar to its relative C. microcalyx (syn. gloriosa), but while the stems of C. microcalyx hang limp or creep along a surface, those of C. crassifolia are rigid. This plant flowers most of the winter and on-and-off during the summer. Like R. ‘Aravir’, it goes outside under shade cloth once the danger of frost is past.

3. Taraxacum albidum (Japanese white dandelion)

When growing dandelions for chicken snacks and salad greens, it’s fun to try unusual varieties. Last year we flowered the pink dandelion (Taraxacum pseudoroseum), and this year white dandelions are getting started. Taraxacum pseudoroseum wasn’t very pink, but T. albidum is definitely a more pure white. Since dandelions can be persistent weeds, we keep them in pots and clip off inflorescences before the seeds are mature.

4. Camellia ‘Rosehill Red’

Not much to say about this; it’s a very nice Camellia japonica cultivar. I tend not to like double and semi-double flowers, but these ones aren’t too fussy looking. It is beside Camellia ‘Yuletide’ which flowers in early winter, so I get an extended shot of red color in that part of the garden.

5. Muscari armeniacum ‘Touch of Snow’

These little guys that I planted last autumn are a little difficult to find in the garden, but they’ll become more obvious as they start to form clumps. They make a nice change from the more typical purple grape hyacinths.

6. Hyacinthus ‘Woodstock’

I had a little trouble finding six flowers that I hadn’t featured before, so I’ll slip in these hyacinths which actually flowered a couple of weeks ago. Like the Muscari ‘Touch of Snow’, I planted them last autumn, so this was my first look at the flowers. My wife was the one who picked them out of the catalog, but I very much like the intense magenta color which darkens to purple at the base of the flower. Quite possibly my favorite Hyacinth now.

Jim at Garden Ruminations is the host of Six on Saturday. Head over there to see his Six for this week and find links to the blogs of other participants.

Ceratostema glans

Ceratostema glans flowers attract many tiny ants, but they are almost certainly pollinated by hummingbirds in nature.

Ceratostema glans is another one of the neotropical “blueberries”, mostly epiphytic members of the Ericaceae which have edible berries (though they may not be blue). This species doesn’t seem to be as floriferous as the Macleania sp. aff. smithiana, but with its unusual flowers and small, semi-succulent leaves on arching stems, it is a very pretty little shrub.

According to Luteyn and Pedraza-Peñalosa, “Blueberry Relatives of the New World Tropics (Ericaceae)“, C. glans grows at 1400 m above sea level in primary rainforest in Ecuador. I purchased this plant from Ecuagenera about a year ago, and it tolerated its first North Carolina summer very well, flowering in April and October and thriving outside under shade cloth in even the hottest months. I have high hopes that this plant will be a long term success.

Rhododendron viriosum hybrids

Rhododendron ‘Festive Bells’

Rhododendron ‘Festive Bells’ is currently flowering in my shade house, so this seems like a good time for a quick post on Rhododendron viriosum hybrids.

R. viriosum is a vireya, a tropical rhododendron, and is one of only two Rhododendron species native to Australia. It has red, bell shaped flowers and is noted for its phenotypic dominance and the vigor that it imparts to hybrids. Hybrids with R. viriosum as a parent almost invariably have bell shaped flowers in some shade of red, and they are usually strong growers. Appropriately, the species name virosum is derived from the same root as the English word “virile”. The species is difficult to locate in the United States, but I am currently growing two first-generation hybrids and have previously grown a third.

Rhododendron ‘Festive Bells’, shown above, is my favorite of the three. My plant, purchased a year ago, is currently blooming for the first time, and the flowers are absolutely amazing. They are some of the best flowers that I have ever seen on a rhododendron, and perhaps on any plant. The color is a pure, intense fire engine red and the flowers have an incredible waxy texture that makes them look as though they are made of plastic. Like many vireyas, R. ‘Festive Bells’ is somewhat lanky with long internodes, but flowers are nicely in-proportion with the plant size. R. ‘Festive Bells’ has R. viriosum as the seed parent, but the pollen parent is unknown.

Rhododendron viriosum x christianae (Bovees V97)

Bovees V97 is an unregistered clone of R. viriosum x R. christianae bred by E. White Smith, former owner the Bovees Nursery in Portland, Oregon. Bovees was for many years the preeminent source of vireya plants in the United States. It closed a few years ago, so I was happy to find this hybrid still offered for sale by Pacific Island Nursery in Hawaii. Genes from R. christianae have imparted orange tones and a more horizontal stance to the flowers, but the plant still has the vigor expected of an R. viriosum hybrid.

Rhododendron ‘Little Maria’

Rhododendron ‘Little Maria’ was a beautiful little plant that grew in my collection for about five years. The cross is R. viriosum x (viriosum x gracilentum). R. gracilentum is a miniature, cool-growing species from the mountains of New Guinea at altitudes of 2000-2745 m above sea level [1]. Despite the double dose of R. viriosum in the ancestry of R. ‘Little Maria’, R. gracilentum is dominant for plant size. A large specimen of ‘Little Maria’ can fit in a 4″ pot, and both leaves and flowers are about half the size of those of R. ‘Festive Bells’ or V97. Unfortunately, R. gracilentum also seems to be dominant for heat tolerance (or lack thereof). Plants purchased from Bovees died very quickly, but I had better luck with cuttings that I rooted in North Carolina. Anecdotally, I have noticed similar results with other vireyas. When vireya plants in my collection die, it often seems to be because the root system has failed catastrophically in the heat. For some reason, roots that have grown in North Carolina seem tougher–perhaps they have different fungal symbiotes or are better adapted to my potting mix.

Eventually, all of my Rhododendron ‘Little Maria’ cuttings died in the summer heat, and I have been unable to replace them. I am hopeful that V97 will do better in our climate, because R. christianae is from more moderate altitudes of 600-1525 m [1]. Since the other parent of ‘Festive Bells’ is unknown, I will just have to hope for the best, but I have already rooted a cutting as insurance.

Reference

1. Argent, G. (2015) Rhododendrons of subgenus Vireya, 2nd edition. Royal Botanic Garden, Edinburgh.