Taisha is the author for this entry.
Today’s photo is of Cistanche tubulosa. It was taken by Ton Rulkens (aka tonrulkens@Flickr) in its natural habitat on a beach near Chocas- Mar (Mossuril District) in northern Mozambique. Thank you Ton for the picture!
Cistanche tubulosa (Orobanchaceae) is an obligate parasite, meaning it relies on a host plant to complete its life cycle. For Cistanche tubulosa, the host plant is often a species that grows in coarse, sandy soils under dry, arid conditions. The germinated seedlings of Cistanche tubulosa lack the tissues of typical eudicot seedlings, such as the radicle (embyronic root), hypocotyl (embryonic stem) and cotyledons (embryonic leaves). Instead, the germinating embryo develops a tube-like organ that comes into contact with the root of the host plant, penetrates it, and forms the primary haustorium. Once it reaches the central core of root xylem of the host plant, the haustorium replaces the metaxylem cells and ensures physical support and nutritional supply for the parasitic Cistanche tubulosa plant. Collectively, the haustorial cells can look pith-like (despite roots being devoid of a pith) due their likeness to parenchyma cells. The tube-like organ that remains exterior to the root develops into a tubercle, which later differentiates into the stem of the parasite. This stem develops underground in the late summer or autumn. It will remain dormant until spring or summer, then eventually project above ground to reveal the spiked inflorescence. After seed set and release, the inflorescence first withers (usually within 2-3 weeks), followed by the underground stem. It is thought that the remaining stem below the withered spike may redevelop the following spring (see: Ilahi, I., et al. 2010. Cistanche tubulosa (Schenk) R. Wight an important medicinal plant occurring in sand dunes of Karak, N.W.F.P., Pakistan. Pakistan Journal of Botany. 42(1):537-547).
This fleshy herbaceous species is distributed in northern Africa, Arabia, and western Asia to Pakistan, India and central Asia. It grows anywhere from 15-150cm tall, but typically between 30-60cm. As the stem and leaves both lack chlorophyll, it can be also classified as a holoparasite (meaning it relies entirely on the host plant for photosynthates). The alternate leaves, in the form of scales, are arranged spirally around the stem. These scales have no well-developed stomata, instead relying on hydathodes for gas and water exchange. The flowers are bluish or crimson-coloured when young, but turn white, yellow or purplish-yellow at maturity.