Palynology of southern African Boraginaceae: The genera Lobostemon, Echiostachys and Echium

Abstract

The tribe Echieae of the subfamily Boragineae (Boraginaceae) is represented in southern Africa by the genera Lobostemon Lehm, and Echiostachys Levyns, endemic to the south‐western Cape region, and two species of Echium L., E. plantagineum L. and E. vulgare L., both introduced weeds of cultivation. Pollen of all these genera was studied and only one pollen type is recognized. Grains are tricolporate, heteropolar and triangular in equatorial view; ora more or less circular and situated towards the broader pole; tectum reticulate with densely spaced lumina; suprateetal nodules are situated at margins of lumina. The P/E ratio varies from 1.08 to 1.63. Genera of the Echieae are sometimes placed in the tribe Lithospermeae. A comparison of the pollen of the studied genera with that of Lithospermum, confirms that the tribe Echieae should be retained. Pollen of Lithospermum is 6–8‐zonocolporate, usually more or less isopolar and with colpi rhombic in outline. The presence of zygomorphic flowers and absence of calciumcarbonate in the fruit wall also support the retention of Lobostemon, Echiostachys and Echium in the Echieae. Pollen grain structure of the southern African Echieae reveals a close relationship between the genera and could support the merging of Lobostemon and Echiostachys with Echium. Lobostemon and Echium can, however, be separated on the position of an annulus. Echium has a minute collar or ring of 5–10 minute, sparingly hairy lobes, very close to the corolla base. Lobostemon and Echiostachys have densely hairy scales, tufts of hair, ridges or protuberances at or near the base of the filaments. Futhermore, the style is 2‐lobed in Echium and simple in Lobostemon.