Plants in general do not have elaborate excretory systems because of their lower metabolism rate as compared to animals and the nature of their waste products. Primarily plant waste product is oxygen and water from photosynthesis which are usually excreted by the leaves. At night plants generate energy through respiration whose by product is carbon dioxide. CO2 is excreted through the leaves. Other waste products are excreted through the bark. You sometimes see some sticky stuff oozing from the bark of certain trees like the acacia. These are some of plants’ waste products. It seems that plants have evolved a simple system of excretion that does not require sophisticated organs like the kidney and the liver.