Several species of Hypericum are used in traditional Turkish folk medicine. Their most medicinally important secondary metabolites are the hypericins, hyperforins, and phenolics.. Here, we determined the ontogenetic, morphogenetic, and diurnal variations in total phenolics contents from H. aviculariifolium subsp. depilatum var. depilatum (endemic), H. perforatum, and H. pruinatum. Plants of wild-growing H. aviculariifolium subsp. depilatum var. depilatum and H. perforatum, and greenhouse-grown H. pruinatum were harvested four times per day during their vegetative, floral-budding, full-flowering, fresh-fruiting, and mature-fruiting stages. They were then dissected into stem, leaf, and reproductive tissues to be dried separately and assayed. The highest level of phenolics in H. aviculariifolium subsp. depilatum var. depilatum and H. pruinatum was found in the leaves, whereas the floral buds produced the greatest amount in H. perforatum. Variations in contents from whole plants fluctuated diurnally, differing among species over the course of ontogenesis, reaching the highest level at floral-budding and tending to increase at mid-day in H. aviculariifolium subsp. depilatum var. depilatum. For H. perforatum and H. pruinatum, contents also were the highest during floral development, although no diurnal fluctuations were observed in those species.