Hydnora africana root growing alongside Euphorbia rootA Hydnora africana that has numerous contacts with a Euphorbia (white) root. The Euphorbia roots form pad like structures. The nature of the underground axis (stem or root?) in Hydnora is not easy to determine with certainty, because there are no close relatives of Hydnora, and Hydnora is highly specialized for parasitism. However, there are reasons to favor the concept that the Hydnora axes are roots rather than stems. The growing tips show no evidence of reduced leaves at all, and there are no reduced leaves adjacent to the bases of the flowers. The five or six longitudinal rows of stubby roots on the axis remind one of patterns of lateral root formation on roots, whereas lateral roots that form on stems of plants don't tend to form neat longitudinal rows. And flowering plants other than Hydnora that are root parasites form roots (as in Orobanche), not underground stems, that interconnect with roots of host plants.
Hydnora africanaFrom Botanical Society of America Online Image CollectionThe flower of Hydnora, when it first opens, has white threadlike structures that cross the gap between the "sepals." The openings between these threads are barely large enough for a beetle to enter. More about that later! Although a beetle may enter a flower, it evidently has difficulty in finding its way out of the flower. This keeps it inside a flower long enough so that the beetle can pick up pollen or deposit pollen on its surface onto the stigmas at the bottom of the floral tube.
Hydnora africana and host Euphorbia caput-medusaeFrom The Botanical Society of America Online image CollectionThe only portion of Hydnora that appears above the ground surfaces is the upper portion of the flower. Much of the flower is below the soil surface. The flower is thick and succulent in texture. The portion of the flower above the ground surface is tubular and has three openings, one of which is shown here. There are three thick structures, which botanically should be called perianth segments, and which might be likened to sepals, that tend to stay united at the top of the flower.
Hydnora africanaFrom Botanical Society of America Online Image CollectionHere are the dung beetles that visited the Hydnora flowers of the plant cultivated in Claremont, California in 1979. Notice their bodies have some whitish hairs on them; pollen could adhere to these hairs. Flowers pollinated by beetles usually have some tissue that offers beetles as food. In Hydnora, that's the whitish tissue on the inside of the "sepals." But beetles don't confine their feeding to such special "bribe" tissues. Beetles eat pollen and then eat the cells of the stigma. Beetle-pollinated flowers usually have an abundance of pollen and an abundance of stigma areas, and Hydnora flowers are no exception. By producing excess pollen and stigma cells, beetle-pollinated flowers succeed in achieving pollination and producing seeds despite the feeding habits of the beetles.
Hydnora africanaFrom the Botanical Society of America Online Image CollectionThe threads that cross the gaps between the "sepals" of the Hydnora flower when the flower opens are pulled apart after a few days. Any beetles that entered the flower through those threads can now easily escape.
