Crassula streyi leaves

Crassula streyi resembles C. multicava. It was even thought to be the same plant at one stage. The first glance difference is the burgundy red lower leaf surfaces of the plant shown here.

The simple, opposite leaves are large, oval in shape with short petioles or sessile and even fused at the base. The leaf margins are entire, curving down and pitted. The leaf-pairs are decussate, successive pairs perpendicular (horizontally) to the previous or next pair on the stem. The blades are thinly fleshy to succulent with small dots scattered densely all over. Pale midribs are sometimes visible, both sunken and ridged above. The bases of a few lateral veins are sometimes visible, ascending a short distance from the midrib before disappearing in the blade. 

A less obvious, but botanically significant difference is the positioning of the guttation glands. In C. multicava these glands are scattered all over the leaf surfaces. In C. streyi they occur only on the leaf margins.

So what are guttation glands? They are specialised pores (also called hydathodes) for exuding surplus watery (xylem) sap including excess dissolved salts. Sometimes the drops seen on leaves in the morning are not dew that has condensed from the atmosphere, but liquid squeezed out of the plant through the leaves. A mild pressure has then built up in the plant overnight from the absorption of more moisture through the roots than needed. This excess can sometimes not be shed by transpiration during the night when the stomata on the leaves may have closed.

Many plants, including some grasses, use this process. Guttation resembles sweating (Smith, et al, 2017; Capon, 2005; Pooley, 1998; iNaturalist; Wikipedia).