Wandering through the E.H. Lohbrunner Alpine Garden in UBC Botanical Garden, I couldn’t help but notice this beautiful, flowering Asphodelus aestivus. The bees were enjoying these flowers as much as I was (or maybe more), but I didn’t manage to get a good photo of the bees flitting in and out of the nectar-rich flowers. Thankfully, Gideon Pisanty is a more patient photographer than I am. He captured a lovely photo of a solitary female bee (Anthophora sp.) on
Asphodelus aestivus, or summer asphodel, is widely distributed across the Mediterranean Basin. It responds well to disturbance; drought, fires, soil erosion and overgrazing have favoured this species. It has become the most prominent species in many Mediterranean ecosystems. Homer coined the term asphodel meadows in the Odyssey, to describe the subterranean meadows of the afterlife. It is hard for me to believe that this species is common, having seen only one specimen of Asphodelus aestivus, lovingly-tended at the UBC Botanical Garden. In the Mediterranean, however, some ecosystems are now described as Asphodel deserts–ecosystems so degraded that they can support little life other than the remarkable Asphodelus aestivus.
Summer asphodel is a geophyte, meaning that it has an underground storage organ (its fleshy root-tuber). This root-tuber has been well-studied by Sawidis et. al. (Flora, 2005), who claim that it is the key to Asphodelus aestivus’ domination of arid Mediterranean landscapes. Asphodelus aestivus experiences two phenological phases each year. From autumn to late spring, the plant is active: its leaf emerges, it flowers, the leaves senesce, and the fruit forms. During this phase, the root-tuber grows and propagates (summer asphodel can reproduce vegetatively as well as sexually). In the summer, the plant retreats to its root-tuber, which undergoes a period of dormancy and can experience significant shrinkage.
Sawidis et. al. analyzed slices of Asphodelus aestivus root-tubers, and found that five functions contribute to their efficacy. Firstly, the root tuber is covered by velamen, a spongy layer composed of multiple epidermis that both absorbs moisture and prevents moisture loss. The velamen cells become filled with water during a rainfall, (these cells are filled with air during periods of drought). Secondly, the inside tissue of the root-tuber (parenchyma) has large water storing cells. Thirdly, the outer portion of the root-tuber (cortex) contains soluble sugars. Fourthly, the cortex contains oil cells with potentially defensive lipids. Finally, isolated plant cells contain raphides, needle-shaped calcium oxalate crystals that cause mechanical and chemical irritation to would-be consumers. Thus, Asphodel aestivus root-tubers contain most of the plant’s biomass at all times of the year, and store large quantities of water and nutrients that are crucial to tempering the seasonality of the Mediterranean climate. Furthermore, the root-tuber’s oil cells and raphides defend it against herbivores that would like to partake in such bounty.
One bounty that summer asphodel does share freely is its nectar. Each Asphodelus aestivus plant produces hundreds of flowers on multiple flowering branches. The flowers open from the base towards the apex. On any given inflorescence, up to 30 flowers may be open each day. The flowers bear six white petals with a dark stripe through their centre. Each flower secretes a large amount of nectar, and is large enough to accommodate insects of various sizes.
It is easy to see why pollinators (honeybees and bumblebees in particular) enjoy visiting summer asphodel, but the hot and dry summer conditions of the Mediterranean do pose some challenges to nectar collection. If nectar is allowed to evaporate from the flower, the remaining nectar becomes too viscous for pollinators to collect. In the article, The secretory glands of Asphodelus aestivus flower (PDF), Thomas Sawidis (2012) found that Asphodelus aestivus solved this problem by discharging its nectar through small holes in the ovary wall. The ovary wall is surrounded by six closely-packed stamens. At the base of these stamens are numerous papillae, or small outgrowths, that create a barrier and protect the precious nectar from evaporation. This abundance of nectar-filled flowers leads to an overproduction of fruit. Asphodelus aestivus can selectively abort excess fruit. This helps provide an insurance policy against unpredictable climate (Sawidis 2012; Johan 1991, The American Naturalist).
For more about the name and anthropogenic uses, see the 2008 Botany Photo of the Day entry for Asphodelus aestivus.