True Toppers

The “eu” of Eucalyptus tells us something is true, real.  The “calyptus” part (from Greek kalyptos) suggests there is a lid, or a cap, involved.  And indeed there is. 

Each bud of a Eucalyptus flower is capped with a Hershey Kisses-looking topper that breaks away around its rim (a kind of opening we call “circumcisal dehiscence”).  We think of the lid as being formed by consolidated tissues derived from sepals and petals, which are not otherwise apparent.  

When a Eucalyptus flower opens, the cap falls off, exposing a gorgeous shock of very handsome stamens (as seen in the accompanying photos of Eucalyptus macrocarpa.)  

This self-decapitating character unites the more than 700 species of Eucalyptus native to Australia and a few other lands in the Southern Hemisphere.  

But the flowers hold more secrets yet, because you’ll not readily encounter an an ovary among those showy stamens.  The Eucalypts, along with other members of the Myrtle family, tuck their ovaries down inside the flower stem, seemingly below the flower itself.  Because the ovary appears to form below the flower, we describe it as “inferior” – implying it is below the petals.  That  normally means any persistent sepals, petals, or anthers will be discovered at the tip of the fruit, as we see in Myrtus and other relatives.

With Eucalypts, the petals and sepals fell off as the cap, and the anthers also abscise, so the mature fruit will be tipped with a ring, evidencing the suture formed when the cap fell off  at anthesis (flower opening).  

In examining Eucalyptus macrocarpa, you’ll note wax covers the entire plant, giving buds, stems, and leaves a blue color.  The wax is exuded to the surface through epidermal cells, and can be rubbed off (see the photos below) with modest effort.  We usually consider production of heavy wax as an adaptation to very sunny and dry habitats.  But wax is not the only special compound we associate with these plants; Eucalypts are often resinous, producing highly fragrant volatile oils.  

There are over 150 different kinds of Eucalyptus growing at The Huntington, each with its own resinous character.  Across North America, people might associate the oil extracted from certain Eucalyptus as one component of the salve called Vicks VapoRub (both registered and trademarked terms), but not all Eucalypts smell so medicinal; in the landscape around the Huntington Mausoleum, you’ll find two large specimens of Eucalyptus citriodora, the Lemon-scented Gum.   Many Californians will recognize this tree for its lemony-fragrance, which pervades the surrounding area.

Leave a comment

Leave a Reply

%d bloggers like this: