Monday, October 10, 2016

Colchicum as a Pollinator Plant

Colchicum cilicicum with Apis mellifera.
Plants that captivate me are simultaneously uncommon in gardens, have unique life cycles, and are attractive to pollinators. One such group of plants that meet this criterion are in the genus Colchicum. Bees and some other pollinators have been captivated by these flowers, which grow from corms (though this is debated, their morphology is unique). Despite the colloquial name, "autumn crocus," some of the 100-150 species bloom in autumn, while many others bloom in winter and spring (and in the genus Crocus, there are many autumn and winter blooming species as well). The most commonly available species and hybrids bloom in the fall without their leaves, while the leaves and seed pods appear in the spring. They are a late source of pollen and nectar, and thus are very attractive to bees and other pollinators.

Colchicum cilicicum growing among Geranium macrorrhizum leaves
Colchicum are primarily bee-pollinated, though flies and perhaps certain wasps may play larger roles in pollination in some districts. The closely related genus Androcymbium has some species that are pollinated by rodents and perhaps birds in their native South Africa. Androcymbium has flowers that are small and held on small pedicels grouped in heads within green or petaloid bracts, lacking any resemblance to Colchicum as it is commonly known. The flowers of Colchicum sensu stricto lack above-ground stems and are therefore weak, held up only by the calyx, thus unfit for pollination by vertebrates. Androcymbium is found mostly in continental Africa with at least one Mediterranean species while Colchicum sensu stricto is native to Europe, North Africa, and Western to Central Asia.

Colchicum cilicicum leaves are pleated but not too large.
The leaves of some species appear in the spring, while others appear in the fall or in winter, sometimes while blooming or just after the flowers fade. Species which flower and leaf out in the winter tend to be native to milder, perhaps maritime, climates that do not get too cold in winter. The species and hybrids I grow are perfectly hardy, flowering in the autumn and showing little signs of growth until spring when the leaves and seed pods emerge. My garden is home not only to me and my garden but to deer, voles, wild turkeys, rabbits, tree squirrels, and red digger squirrels (among others) and the colchicums are ignored by all of these herbivores, both above and below ground, at least in part due to toxic alkaloids within the plants. Slugs are a minor nuisance, occasionally eating parts of the leaves, but never enough to cause concern.

Colchicum cilicicum with Apis mellifera
Why flower in autumn? There are a number of reasons why some species of Colchicum have adapted to flowering in the fall, winter, or spring. All geophytes (which possess at- or below ground storage organs; i.e. tubers, bulbs, etc.) have the advantage over non-geophytes of flowering outside of the typical growing season, and/or when conditions are not ideal for growth (too cold, dry, etc.) by using stored energy rather than waiting for optimal conditions. This results in less competition by other plants, and enticing (or forcing?) pollinators to visit their flowers. Large showy flowers in a part of the year that is otherwise scarce or devoid of other flowers is a huge advantage. This is apparent in my garden where multiple species of bees and flies visit the few specimens I grow. At any other point in the year, a single specimen of a given plant species is unlikely to attract pollinators, especially a diversity of pollinators, because pollinators in general are more interested in large groups of flowers. Autumn blooming species seem to be the exception to the rule.

Below are a few selected fall blooming species and hybrids from my own garden and abroad, with photos by Ian Young (Scotland), Gideon Pisanty (Israel), and myself (SW Oregon), with an emphasis on pollinators:

Colchicum stevenii with Andrena sp. (Photo by Gideon Pisanty, 2009)
Colchicum stevenii is a Mediterranean species native to Cyprus across Southern Turkey to Syria, Jordan and Israel. It grows on rocky slopes and dry banks and blooms from October to December, flowering beginning after the first fall showers. The leaves often appear with the flowers or sometimes as the flowers fade. Usually, only one or two flowers appear from each corm, but clumping individuals may produce bigger displays. Colchicum stevenii is a widespread species where it is native, though not oft grown in gardens. These photos by entomologist, researcher, and photographer Gideon Pisanty of Tel Aviv University show Colchicum stevenii in its native habitat in Israel being visited by native andrenid bees.

Colchicum stevenii with Andrena sp. (Photo by Gideon Pisanty, 2009)
Colchicum stevenii produces some nectar, but it is in small quantities and is dilute (low sugar content). To make up for this it produces pollen in good quantity, yet the species is polymorphic, having at least five distinct forms. Stigma length varies from short (below anthers), medium (level with anthers), and tall (higher than anthers) in addition to having both female (lacking anthers) and male (lacking stigma) forms. Different pollinator types visit each form. In one study (Dafni 1996) solitary bees and honeybees were observed to be most attracted to forms with short stigmas, while syrphid flies were most interested in flowers with long stigmas. Solitary bees were found to be more interested in the nectar than honeybees, and I would guess this to be due to the typically smaller body size of solitary bees than honeybees.

Colchicum 'Lilac wonder' with Halictus ligatus
A more accessible and commonly grown colchicum is the hybrid Colchicum 'Lilac Wonder'. It is an old hybrid dating from at least 1926, if not earlier, and speculated to be the progeny of C. giganteum and C. bornmuelleri (both occasionally considered synonyms of the variable C. speciosum), or possibly C. speciosum and C. bivonae (a species commonly used in breeding efforts). Whoever the parents are, this hybrid has very large flowers that can span five inches across when fully opened, and stand ten inches tall. This leaves it susceptible to mechanical damage from wind, rain, or animals (including children, like my three year old), leaving them laying flat like deflated balloons after the kids birthday party.

Colchicum 'Lilac wonder' with my hand for scale
Perhaps as a result of it being a hybrid, 'Lilac Wonder' seems to produce pollen in only small quantities which lessens its usefulness to pollinators. Despite this, it is still visited by a variety of bees. In my observation this is usually honeybees, but native bees occasionally visit these. I have not seen bumblebees visit the colchicums, though this is most likely because the Bombus species in my area are not active at this time of year with the exception of a few of next years queens.

Colchicum 'Lilac Wonder' with Toxomerus marginatus
Flower flies, such as syrphid flies, primarily feed on pollen and so are attracted to the anthers of Colchicum. Most of the floral visitors that visit the colchicums in my garden are interested in the pollen, while very few are interested in the nectar. I wonder if most species have poor quality nectar like C. stevenii, or if that is variable between species or climate. Note the lack of pollen on the anthers of C. 'Lilac Wonder' compared to the easily visible pollen in the photos of C. stevenii and C. cilicicum.

Colchicum speciosum
Another Colchicum I grow is C. speciosum, a commonly available species that is used frequently as a parent of new hybrids. For me, it is the first to bloom, but it does not seem to thrive in my USDA zone 7 climate. It does not seem to be as attractive to pollinators in my garden, either.

Colchicum speciosum with Eupeodes sp. (top) and Eristalis sp. (bottom) (Photo by Ian Young, 2016)
Halfway across the world, in the garden of Ian Young in maritime Eastern Scotland, Colchicum speciosum seems to perform much better. This could be climate, or it could be that the species is grown by a gardener with more skill than I. Flower flies in the family Syrphidae often have similar colors and markings to bees and wasps, possibly warding off some predators expecting a stinger which they do not possess. Most of these flies feed on pollen but they will also feed on easily accessible nectar. Colchicum has nectar that is only accessible to insects with a proboscis long enough to reach it, and most flies have short proboscises that are better suited to shallow flowers such as those found in the Apiaceae (carrot family). Pollen then, it would seem, is the primary reward to pollinators in Colchicum.

Colchicum speciosum leaves
Leaves of the many species can vary quite a bit in appearance. These are the leaves of Colchicum speciosum in my garden, compare to the leaves of C. cilicicum above. Some species, like C. montanum, have very thin strap-like leaves that are more comparable to the leaves of Muscari than C. speciosum or C. cilicicum

Colchicum montanum with Eupeodes sp. (hoverfly) (Photo by Ian Young, 2006)
Colchicum montanum (syn. Merendera montana) is a European species native to the Central Pyrenees and Iberian peninsula from 900 to 2500m. It grows in grassland and rocky slopes, and is often grown in rock gardens and alpine houses (photos seen here by Ian Young in his bulb house). I speculate that flies are the primary pollinators, being a high altitude species, where flies are more reliable pollinators than bees (although both are present) in alpine and tundra environments. This would account for the comparatively equal length, yet short, reproductive parts.

Colchicum montanum with Eupeodes sp. (hoverfly) (Photo by Ian Young, 2006)
Colchicum montanum shares its environment with the Mediterranean pine vole (Microtus duodecimcostatus) which, despite the toxic alkaloids in the corm, eat the corms. This actually seems to enhance the fitness of C. montanum by spreading small corms about and reducing competition between individuals. The species seems to lack a seed dispersal method that separates plants, so the voles may be playing a role in inadvertently distributing the corms once established.

Colchicum (bivonae?) hybrid with Vespula vulgaris (Photo by Ian Young, 2004)
Ian Young grows a number of colchicums, species and hybrids, in his garden in Eastern Scotland. Photographed here is an old hybrid, at least two decades old, with a common yellowjacket, Vespula vulgaris. The name of this hybrid is long lost, although it bears a resemblance to Colchicum bivonae which has been used as a parent to many hybrids lending to them its petal tessellation.

Colchicum (bivonae?) hybrid with Vespula vulgaris (Photo by Ian Young, 2004)
While wasps are probably less frequently seen visiting colchicums than bees or flies, but they are nonetheless important pollinators for some plants. Except for a few exceptions (Masarinae, pollen wasps) adult wasps feed solely on nectar and do not collect pollen for their offspring, opting instead for other arthropods as a source of protein for developing larvae. Adult wasps, like bees, require carbohydrates to fuel their active lives and nectar fills this requirement. Wasps aren't as picky about the quality of nectar as bees are, and may be more willing to visit plants that produce nectar of a lower quality. I suspect that is the case here, considering the level of rainfall in this part of Scotland could have raised the level of the nectar to a level easily accessible to this unspecialized nectar-drinker, simultaneously diluting it.

Colchicum cilicicum with Apis mellifera
Colchicum cilicicum is native to Turkey, Syria, and Lebanon in forest margins, rocky slopes, and stream banks, often growing in limestone. It is probably one of the more commonly available species in the horticultural trade, which probably results from its ease of growth. I find this species to be the most reliable performer in my garden, and while it has smaller flowers than the others, it is my favorite. It makes up for the smaller size of its flowers by sending up many of them, and clumping readily. Add to this the long bloom period, about a month for this single clump, even though individual flowers only last a few days. The flowers are short, which means they are less easily knocked down.

Colchicum cilicicum with Halictus ligatus
Various bees and flies have visited the flowers of C. cilicicum, as well as carpenter ants (Camponotus sp.) seeking the sugary nectar. Pollination is always achieved by some means, most likely by insects, as apparent by the full seed pods it sends up every year.

I hope you will give this genus a try in your own garden, or find a way to see them in the wild. Corms are usually available for sale in the fall along with other spring blooming bulbs, corms, and tubers (See my Links for a few sources)

Dafni, Amots. "Autumnal and winter pollination adaptations under Mediterranean conditions." Bocconea. 5.171-181 (1996) 
Gómez-García, Daniel, José Azorín , Stella M. Giannoni and Carlos E. Borghi . "How does Merendera montana (L.) Lange (Liliaceae) benefit from being consumed by mole-voles?." Plant Ecology. 172.(2004): 173-181. 
Kleizen, Ciara, Jeremy Midgley and Steve D. Johnson. "Pollination Systems of Colchicum (Colchicaceae) in Southern Africa: Evidence for Rodent Pollination." National Center for Biotechnology Information. Ann Bot. 2008 Nov; 102(5): 747–755 
Piling, David, et al. "Colchicum." PBS Wiki. Pacific Bulb Society, 22 Jan 2016. Web. 
Pisanty, Gideon and Yael Mandelik . "Effects of alien species on plant-pollinator interactions: how can native plants adapt to changing pollination regimes?." Evolution of Plant–Pollinator Relationships. Cambridge University Press. Chapter 15.(2012): 414-438. 
Rader et al.. "Non-bee insects are important contributors to global crop pollination." Proceedings of the National Academy of Sciences. 113.1 (2015): 
Sütlüpinar, N. "The evaluation of Turkish autumn flowering Colchicum species." Journal of Faculty Pharmacy of Istanbul University 32 (1998): 1-8.
Young, Ian. "Bulb Log 36." SRGC Bulb Log Diary. Scottish Rock Garden Club, 8 Aug 2004.
Young, Ian. "Bulb Log 37." SRGC Bulb Log Diary. Scottish Rock Garden Club, 13 Sep 2006.