August 7, 2009 11 Comments
I encountered few insects this past June on the dry slopes of sand shinnery oak shrubland that just makes it into the northwestern corner of Oklahoma’s Four Canyon Preserve - insect population levels were still depressed from the wildfire that swept through the area in April of last year. Plant life, however, was diverse and abundant, including this most unusual plant – Krameria lanceolata (many common names, including trailing krameria, trailing ratany [sometimes spelled "rhatany"], Texan ratany, prairie sandbur, sandspur, etc.). A dicot in the monogeneric family Krameraceae, plants in this genus share several unusual traits, the most obvious being their distinctly orchid-like, zygomorphic flowers (i.e., capable of division into symmetrical halves by only one longitudinal plane passing through the axis). The resemblance to orchids is strictly superficial – they are most closely related to plants in the family Zygophyllaceae.
Orchids, of course, are monocots with trimerous flowers that only appear to be five-petaled because of the three petal-like sepals and the third true petal being modified into a “lip” onto which pollinating bees land. Krameria flowers also appear five-petaled with a lip, but in this case it is the five sepals that form the “petals,” while the five true petals are modified into a lip (three fused petals) and two lateral upright “flags” called elaiphores. These eliaphores play a central role in Krameria‘s unusual pollination biology, whose flowers produce not nectar, but fatty oils as rewards for their visitors – female bees of the genus Centris (Anthophoridae) (Simpson and Neff 1977). The bees collect the oils from the modified external surfaces of the eliaphores, pollinating the flower in the process, and mix the oils with pollen to feed their larvae. Although the Krameria plants are wholly dependent upon Centris bees to effect their pollination, the relationship is not mutually exclusive – Centris bees utilize other oil-producing plants as well.
All species of Krameria examined to date are obligate semiparasites, forming haustoria on the roots of a broad range of host plants. Of the 18 species currently known in the genus, five occur in the U.S., with K. lanceolata the most widespread (Kansas and Colorado south to Arizona, New Mexico, and Texas and east to Georgia and Florida) (Austin and Honeychurch 2004). It is distinguished from the other U.S. species by its herbaceous, prostrate form.
Update 8/10/09: Mike Arduser, my hymenopterist friend who visited Four Canyon Preserve with me, wrote the following in response to my query about collecting bees from these flowers:
Yes, collected several off Krameria at Four Canyons and at Packsaddle – all were the same species, and I’m trying to remember the name as I’m writing this (all notes and material are at home) – it was Centris lanosa. They are best found by listening, as they have a distinctive buzz as they move from flower to flower at ground level (difficult to see there).
Austin, D. F. and P. N. Honychurch. 2004. Florida ethnobotany. CRC Press, Boca Raton, Florida. 909 pp.
Simpson, B. B. and J. L. Neff. 1977. Krameria, free-fatty acids and oil-collecting bees. Nature 267: 150-151.
Copyright © Ted C. MacRae