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.

Ang_sesquipedale2

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’

Six on Saturday #62 (January 2, 2021)

flowers of Macleania sp. aff. smithiana
Macleania sp. aff smithiana

2021 has started cloudy and damp, and since we have already had several hard freezes this winter, there isn’t much that’s growing outside apart from a some cold-weather greens in the vegetable garden. This Six on Saturday is, therefore, a grab bag of tropical plants from my greenhouse.

1. Paphiopedilum purpuratum

Paphiopedilum purpuratum flower

Paphiopedilum purpuratum is a small slipper orchid native to Hong Kong and adjacent mainland China. According to the IUCN Red List, it is critically endangered, with fewer than 250 individual plants surviving in the wild. Despite its rarity in the wild, it is well established in cultivation, and artificially propagated seedlings like this one are relatively inexpensive, making it even sadder that the wild plants are still collected for unscrupulous horticulturalists.

2. Hippeastrum puniceum ‘Ibitipoca’

flower of Hippeastrum puniceum

Ibitipoca is a locality in Minas Gerais state, presumably where this clone of H. puniceum was originally collected.

3. Burbidgea schizocheila (golden brush ginger)

flowering plant of Burbidgea schizocheila

This very attractive dwarf ginger, endemic to Borneo, was once difficult to find in cultivation, but it is now being mass produced and shows up at local garden centers. I keep it outside in the summer, and it seems to flower mostly in winter without a prolonged dormant period.

4. Cavendishia capitulata (Huntington Botanical Gardens #92102)

flowering branches of Cavendishia capitulata

Flowering for the first time after growing for five years in my greenhouse, this pretty little shrub is an epiphytic member of the blueberry family (Ericaceae) from Costa Rica, Panama, and northern Colombia. Like the Macleania species that I have previously discussed, its flowers are pollinated by hummingbirds. I really love the fantastic shapes and colors of the neotropical Ericaceae, and I hope that the Cavendishia will prove to be as floriferous as the Macleania, which flowers almost nonstop now that it has reached a decent size (see photo at top of this page).

5. Nepenthes tobaica

Nepenthes tobaica pitcher

See Six on Saturday #12 for more information about Nepenthes pitcher plants. N. tobaica is a smallish species endemic to the region around Lake Toba on the island of Sumatra. My plant is still fairly young and only recently started producing fully mature pitchers.

6. Nepenthes rafflesiana

Nepenthes rafflesiana lower pitcher

N. rafflesiana is a much larger species with a wider native range encompassing Borneo, Sumatra, Singapore, and penisular Malaysia. Compared to the clone that I previously photographed (see picture 5), this seed-grown plant has more squat lower pitchers, and I prefer its more evenly distributed red speckling and dark red petioles.

The Propagator 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.

Pseudoscorpion

pseudoscorpion
Pseudoscorpion found on an oak log. Scale = millimeters

This isn’t a very good photo, but I am very excited to have finally found a pseudoscorpion, thirty or more years after I first read about them. Pseudoscorpions are arachnids, like spiders and true scorpions, and they are found in a wide variety of habitats worldwide–including at least one species that likes to inhabit old books, where it feeds on booklice. They are part of the complex world of tiny animals that fills every garden but is largely unseen, even by the most observant gardeners.

The largest pseudoscorpion species is only about a centimeter long, and most of the 3000+ species are only a few millimeters long. Unlike true scorpions, they lack a tail with venomous stinger, and instead they have venom glands connected to their pincers. But don’t fear; the venom is only a cause for concern if you are a tiny creature like a mite or a springtail that the pseudoscorpion might like to eat.

I found this pseudoscorpion while I was hammering wooden plugs inoculated with shiitake mycelia into some fresh oak logs to expand my mushroom garden. I suddenly noticed a tiny creature scurrying across the bark near my mallet. At first glance, I wondered if it might be a newly hatched tick, but its movement didn’t seem quite right. As soon as I looked a little more closely, I knew exactly what it must be. Unfortunately, it is right at the edge of my camera’s focusing ability, but I’m glad to have some sort of permanent record even if it is a but blurry. Maybe I should get one of those little macro lenses for my iphone, in case I find another one in the next thirty years.

pseudoscorpion with millimeter scale

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.