Lord Rothschild and Saint Swithin

Paph_rothschildianum1
Mature Paphiopedilum rothschildianum can have 4-6 flowers on an inflorescence, so this plant with three flowers is still just a baby.

With its large, elegant flowers on an upright inflorescence Paphiopedilum rothschildianum is one of the most magnificent slipper orchid species, and it caused a sensation when introduced into cultivation in 1887. At first, its habitat was falsely said to be in New Guinea, probably to throw competing plant collectors off the trail, but although its true origin in Borneo was correctly reported in 1895, it was long considered extinct in the wild. The species was finally rediscovered 1959, when it became clear that wild populations are restricted to the vicinity of Mount Kinabalu. Of the three sites discovered, one has subsequently been completely destroyed by fire, leaving only two sites that are both within Kinabalu National Park [1]. P. rothschildianum once had a reputation for being very slow growing and reluctant to bloom, but selective breeding has produced plants that grow at a reasonable speed and are not particularly difficult to flower. These artificially propagated plants are much to be preferred to wild plants that are sometimes still poached from the park.

P. rothschildianum was named in honor of Baron Ferdinand de Rothschild, a Victorian banker, politician, art collector, and orchid grower, making it a member of a select group of orchids named for the Rothschild family. The other members of that club–Eurychone rothschildiana, Ancistrochilus rothschildianus, Bulbophyllum rothschildianum, and Vanda Rothschildiana–are all fantastic plants.

Paph_rothschildianum2
The hook-shaped staminode of P. rothschildianum is covered with glandular hairs. It has been suggested that the hairs mimic an aphid colony to attract the predatory hoverflies which pollinate the flower [2].

Paphiopedilum Saint Swithin

Paphiopedilum saint Swithin inflorescence with four flowers
Paphiopedilum St Swithin, first bloom seedling with four flowers on a single growth.

Paphiopedilum Saint Swithin (P. philippinense x P. rothschildianum) was one of the earliest P. rothschildianum hybrids, and it is still one of the best. It was registered in 1900 by Thomas Statter, who three years earlier had also registered the famous cross of P. rothschildianum x P. stonei as P. Lady Isobel. Unfortunately, orchid hybrid registrations, unlike species descriptions, do not include an etymology section. While it was possible to deduce the identity of Lady Isobel (and correct a 120-year-old spelling error), it is unclear why Statter named a tropical slipper orchid after an Anglo-Saxon saint. Perhaps it first flowered on July 15, St Swithin’s Day, or perhaps Statter had some connection to one of the many schools and churches dedicated to St Swithin/Swithun.

What is clear is that P. St. Swithin is an excellent example of heterosis, the tendency of F1 hybrids to be more vigorous (larger, faster growing, more robust) than either parent. The flowers are somewhat variable, depending on the P. philippinense parent, but they are almost always good quality. My plant was bred using P. philippinense var roebelenii (see photo 1 here for an example), and that parentage is reflected in its long drooping petals. I have also seen plants with shorter petals held at a roughly 45-degree angle, which were presumably bred using P. philippinense plants with shorter petals.

References

  1. Van der Ent, A., Van Vugt, R., and Wellinga, S.M. (2015) Ecology of Paphiopedilum rothschildianum at the type locality in Kinabalu Park (Sabah, Malaysia). Biodiversity and Conservation 24:1641–1656
  2. Atwood, J.T. (1985). Pollination of Paphiopedilum rothschildianum: brood-site deception. National Geographic Research 1: 247-254.

Darwin’s Orchid

Angraecum_sesquipedale
A seedling of Angraecum sesquipedale flowering for the first time.

“The Angraecum sesquipedale, of which the large six-rayed flowers, like stars formed of snow-white wax, have excited the admiration of travellers in Madagascar, must not be passed over.  A green, whip-like nectary of astonishing length hangs down beneath the labellum.  In several flowers sent to me by Mr. Bateman, I found the nectaries eleven and a half inches long, with only the lower inch and a half filled with nectar…in Madagascar there must be moths with proboscides capable of extension to a length between ten and eleven inches. This belief of mine has been ridiculed by some entomologists…”

  — Charles Darwin, 1862, On the Various Contrivances by Which British and Foreign Orchids Are Fertilised by Insects, and On the Good Effects of Intercrossing.

Next Friday, February 12, is Charles Darwin’s birthday and not coincidentally is also Darwin Day, commemorating the great man’s myriad contributions to science. It is therefore appropriate that my Angraecum sesquipedale, commonly called Darwin’s orchid, is flowering this week. Darwin’s prediction of a sphinx moth with a prodigious proboscis was elaborated by Alfred Russell Wallace in 1867, but Darwin was not proven correct until 1903. The moth in question, a subspecies of the African Xanthopan morganii, was named X. morganii praedicta, and it was finally photographed in the act of pollinating an Angraecum in 1992.

In his discussion of the pollination mechanism of Angraecum sesquipedale, Darwin suggested that the plant would be most efficiently pollinated if a moth were forced to push against the flower as it stretched for nectar at the bottom of a nectary that was lightly longer than the moth’s proboscis. On the other hand, a moth would be more likely to obtain nectar if its proboscis were longer than the nectary:

“As certain moths of Madagascar became larger through natural selection…or as the proboscis alone was lengthened to obtain honey from the Angraecum and other deep tubular flowers, those individual plants of the Angraecum which had the longest nectaries, and which, consequently, compelled the moths to insert their proboscides up to the very base would be best fertilized. These plants would yield the most seed, and the seedlings would generally inherit long nectaries; and so it would be in successive generations of the plant and the moth. Thus it would appear that there has been a race in gaining length between the nectary of the Angraecum and the proboscis of certain moths.”

Angraecum-closeup
Entrance to the nectary. Darwin recognized that if a moth is forced to stretch for nectar, its proboscis will be more likely to slide into the notch in the column and the moth’s head will come in contact with the pollinia hidden under the round anther cap.

More recent research suggests that Darwin’s hypothesis was at least partially correct (for review, see Johnson S.D. and Anderson B., 2010, Coevolution Between Food-Rewarding Flowers and Their Pollinators, Evolution: Education and Outreach 3: 32–39). Experimentally shortening the nectaries of other moth-pollinated flowers has confirmed Darwin’s hunch that they are most efficiently pollinated when the nectary is longer than the pollinator’s proboscis. It is also clear that there is an advantage in having a proboscis long enough to reach all of the nectar in deep flowers. However, flowers and pollinators may not be the only players in this evolutionary scenario. Darwin forgot predators.

When a sphinx moth with a very long proboscis feeds from a shorter nectary, the moth can maintain its distance from the flower and often engages in behavior called “swing-hovering”. This side-to-side movement is thought to be a response to predators, including spiders, which could trap a moth that is immobilized against a flower (Wasserthal L.T., 1997, Botanica Acta 110: 343–59). Thus, predators might drive the evolution of proboscis length sufficient to allow swing-hovering while feeding, and proboscis length would drive the evolution of longer nectaries–which would then drive the evolution of an even longer proboscis, if the longer nectary made moths with shorter proboscises more vulnerable to predation. This predator hypothesis remains unproven in the absence of direct observation of spiders or other predators attacking sphinx moths on Angraecum flowers. However, there is this:

crab spider attacking a butterfly
A crab spider in my garden demonstrating that it can capture butterflies and moths considerably larger than its own body.

Quite apart from its fascinating position in the history of science, Angraecum sesquipedale is worth growing for its beautiful flowers and nocturnal fragrance. It isn’t a particularly difficult orchid to grow and will thrive if given Cattleya light and Phalaenopsis temperatures. Angraecoids notoriously dislike root disturbance, so it is best to use a potting mix that will last a long time. My current plant is in a mix of coarse Orchiata (Pinus radiata bark) and red lava rock, but I have also grown plants successfully in pure lava rock.

There seem to be two forms of the species with distinct flowering times, but it is not always obvious which form is being sold by a particular nursery. One form flowers in winter (late December-February) and the other in spring (often around Easter), but there are no significant morphological differences between the two forms. The winter-flowering form is sometimes in bloom for Christmas (hence its alternative common name, star of Bethlehem orchid), but I have more often seen the hybrid Angraecum Veitchii (A. sesquipedale x A. eburneum) flowering in December.

A. sesquipedale eventually becomes very large and ungainly, but seedlings start flowering relatively young and small. One way to avoid having your growing area swallowed up by a giant Angraecum is to replace your plant every five or six years. Sell the big plant, buy a small seedling, and pocket the price difference.

Angraecum sesquipedale-spring blooming form photgraphed in about 2005
A larger plant of the spring-blooming form of Angraecum sesquipedale that I was growing about fifteen years ago.

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Loooooong petals

inflorescence of Paphiopedilum Michael Koopowitz
Seedling of Paphiopedilum Michael Koopowitz flowering for the first time. Its petals are at least 40 cm long.

Paphiopedilum Michael Koopowitz is a primary hybrid of Paphiopedilum philippinense and Paphiopedilum sanderianum, the two species in the genus with the longest petals. P. philippinense var. roebelenii has impressively long twisted petals (see photo 1 in Six on Saturday #55), but P. sanderianum is in a class by itself–its petals can be up to one meter long. The petals of P. Michael Koopowitz are intermediate between the two species, never approaching the length of P. sanderianum but still long enough to impress. Various fanciful explanations for the long petals of these slipper orchid species have been devised (ladders for ground-dwelling insects?!), but the current hypothesis (if I correctly remember a paper I can no longer locate) is that they make the flower more visible to flying insects. Insect compound eyes aren’t great at making high resolution images, but they readily detect the motion of petals twisting and drifting on the slightest breeze.

P. philippinense var. roebelenii was described in 1883 and P. sanderianum in 1886, but their hybrid was not registered until 1993, despite it being an obvious cross to make. The reason for this century-long delay is that P. sanderianum was lost in cultivation and believed extinct in the wild for most of the 20th century. It was rediscovered in northern Sarawak in 1978, and plants started trickling into cultivation in the 1980s. When I started growing orchids in the mid 1990s, seedlings of P. sanderianum and its hybrids sold for eye watering prices–far out of the reach of my student budget–but near blooming-size seedlings can now be readily obtained for less than $100. That’s still expensive for a plant, but on par with other multifloral slipper orchids.

This seedling P. Michael Koopowitz has grown much faster and flowered earlier than a seedling P. sanderianum that I purchased at the same time (hybrid vigor, yeah!). The inflorescence has three flowers with 40-cm petals, which isn’t bad for a single-growth plant. If all goes well for the next few years, I can hope for inflorescences with four or five flowers, and perhaps longer petals, when the plant has a few more growths.

Paph_Michael-Koopowitz-2
Another view. The parents of this plant are P. philippinense ‘Super Twister’ and P. sanderianum ‘Lady in Red’

Giant Peruvian daffodil

Paramongaia1
Paramongaia weberbaueri

eBay can be a wonderful source for rare and unusual plants, but there’s always a chance you won’t get what you expect. I bought this plant in 2014, and it arrived as a small dormant bulb with no distinguishing characteristics. It could have been almost anything, and I had to wait 6 1/2 years to find out if I got an excellent deal on a very rare bulb, or paid way too much for a mislabeled Narcissus. In this case, I can breathe a sigh of relief, because the plant was as advertised.

Paramongaia weberbaueri is, despite its common name, not a daffodil. It is in the same family as daffodils, the Amaryllidaceae,, but while daffodils are native to the Mediterranean region, Paramongaia is from South America–specifically western Peru, where it grows in the rain shadow of the Andes. There are apparently two forms of the species, a high altitude form which grows and flowers in summer, and a winter-growing lowland form. My plant is obviously the winter-growing form. I keep it in a bright spot in the greenhouse year-round (minimum winter temperature 60 F, 15 C; summer maximum 93 F, 34 C). During winter I water at least once a week, or more frequently if the soil dries out. Then I leave it completely dry, no watering whatsoever, all summer long. Presumably, the humidity in the greenhouse is sufficient to keep the bulb from desiccating while dormant.

The flower bud developed relatively slowly for an Amaryllid and lasted just under a week in good condition. The fragrance was wonderful.

So far, my plant has shown no tendency to produce offsets. The anthers failed to produce pollen–or dried up prematurely, I’m not sure which. In any case, I was unable to self-pollinate the flower.

Paramongaia2
Paramongaia weberbaueri, whole plant with juvenile Homo sapiens to show scale.

Outside and inside

Here are two plants that have almost nothing in common, except that they both flower in late November.

Crocus cartwrightianus var. albus

Crocus cartwrightianus is a small autumn-flowering bulb that is native to mainland Greece and the Cyclades. It is a fertile diploid species and is thought to be the wild ancestor of the sterile triploid Crocus sativus, the cultivated saffron crocus. The typical color form is purple, but I love the contrast of the bright orange stigma with the sepals and petals of this white-flowered variety. C. cartwrightianus grows fairly well in this climate, but the flowers are often damaged by slugs when we have a warm, humid autumn.

Paphiopedilum fairrieanum

While C. cartwrightianus is flowering outside, Paphiopedilum fairrieanum is flowering inside my greenhouse. P. fairrieanum is native to the foothills of the Himalayas in northeast India and Bhutan, where it experiences a summer-monsoon climate. To mimic these natural conditions in cultivation, it should be kept warm and watered well in summer and then given a cooler, drier rest in winter, when temperatures can drop as low as 45-50 F (7-10 C). In my greenhouse, the thermostat is set to 60 F, and the plant probably doesn’t experience temperatures below 55 F (13 C).

With its small, slightly nodding flowers and delicately down-swept petals, P. fairrieanum has an elfin or fairy-like quality that has intrigued orchid growers since its discovery in the mid-1800s. You might think that the species name alludes in some way to the plant’s appearance, but in fact, the species was named after a Mr. Fairrie who flowered the plant that John Lindley used for his species description in 1857.