Morphological and anatomical features of Cuscuta pedicellata and C. campestris

Abstract

Observations on morphological and anatomical features of Cuscuta pedicellata and, to a lesser extent, C. campestris have been made at different stages of their life‐cycles. The seedling is filiform with a bulbous radicular end which collapses early. The simple shoot apex is green and photosentitive. Initial “nutation” is followed by “creeping” over the substrate. Host plants less than about three weeks old seem not to be attacked by Cuscuta seedlings. When haustorial contact is established the shoot apex differentiates into buds and scale leaves. The chlorophyll disappears and stomata, which are lacking in the seedling, develop. The apical growth rate increases strongly by frequent cell division and ‐ elongation. This is reflected anatomically by the formation of “cell families” in rows. Weakening and flowering of the host plants are followed by flowering of the parasite. Greening of stem segments of Cuscuta occurs during formation of haustoria and after death of the host. Stem anatomy is characterized by a tripartite cortex in which the middle layer consists of thin‐walled angular cells. Characteristic are also the voluminuous intercellular spaces, the cortical and perivascular laticifers, and the central position of the small vascular bundles. Observations on self‐parasitism were made. The epidermis of the haustorial cushion elongates and the cytoplasm is mainly positioned towards the host. Pseudo‐intercellular spaces are formed between the epidermal cells. The haustorium connects the phloem of the two plants, but vascular elements of any kind have not been observed.