3.3 Hydathode anatomy and distribution
The anatomy of hydathodes in the Crassula species examined was rather conserved (Fig. 6 ). They all displayed the anatomical arrangement typical of epithemal hydathodes, with three main components: water pore(s), epithem and tracheids. The water pores consisted of more or less sunken pairs of guard cells, which were partially concealed by subsidiary cells. The epithem appeared as a mass of small achlorophyllous cells (Fig. 4 ) underneath the water pore(s), with cytoplasmic contents such as nuclei noticeably stained (Fig. 6 ). A loosely arranged array of xylem tracheids irrigated the epithem and connected it to the leaf vasculature. Cells containing tannins were observed in association with the hydathodes (Figs. 4, 6 ), forming a more or less continuous sheath in some species (e.g.C. ovata ). Anthocyanin contents in hydathode sheath cells were observed in C. perforata and C. ausensis (Fig. 4 ).
Two types of hydathodes (sensu Martin and von Willert 2000) were observed (Table 2 ). Type I hydathodes, characterized by being larger and having numerous water pores within a more or less circular epidermal area, were observed in C. multicava and C. ovata(Figs. 5, 6 ). These hydathodes were also associated with a mineral crust, observed with both light and electron microscopes (Figs. 3–5 ). The remaining species exhibited type II hydathodes, which tend to be smaller and with a single large water pore, often with bulging subsidiary cells (Figs. 4–6 ). The water pores of these hydathodes were located, if present, within the aforementioned papillary/trichomic/idioblastic clusters and/or surface tubercles. The foliar distribution of hydathodes varied among species (Table 2 ), yet they always occurred more abundantly, or even exclusively, on the surfaces most exposed to the atmosphere.