I mentioned last week that you could possibly find a rhododendron in bloom every day of the year in UBC Botanical Garden. I think (and others will surely correct me if I’m wrong) that the only genus of plants that you are guaranteed to find in flower every day of the year is Rosmarinus or the rosemarys.
The olfactory properties of Rosmarinus have a long-standing reputation for being memory stimulants. In “Aromas of rosemary and lavender essential oils differentially affect cognition and mood in healthy adults.” (Int. J. Neurosci. 2003 Jan;113(1):15-38), Moss et al. found evidence that partly supports this assertion, though they also discovered that the scent of rosemary seems to impair speed of memory.
For more on this plant as a spice, I’ll direct you to Gernot Katzer’s page on Rosmarinus officinalis.