What’s an Orchid’s Favorite Number?

My current orchid fam.

My kitchen table is my orchid flex spot. When my orchids bloom, that’s where they go for maximum visibility—I want to see them as many times as possible over the days, weeks, and months in which they’re flowering. Sometimes, like right now, my kitchen table is crowded with flowers (those colder nights really do induce blooming!) When the afternoon light comes in through the window, it illuminates the petals, and I constantly notice new details about the shapes of the tendrils, the cups of the petals, the arrangement of color. 

The other day, I noticed something that’s probably obvious to most people, but for whatever reason had escaped my attention: all of my orchids have what looks like five petals. Regardless of age, shape, or species, the petal arrangement was strikingly similar. I’m not sure why this surprised me—roses look like roses, daisies look like daisies, so why not orchids? Perhaps it’s that some 38,000 species exist, and I assumed that some fairly significant structural differences must exist between them. Or maybe it’s because most flowers don’t have a specific number of petals they grow each time—daisies usually have 15-30 petals and roses usually have 20-40. What kind of flower pushes out five petals and says okay, that’s that? 

Orchid anatomy, via Wikipedia.

Wild roses produce only five petals, as do hibiscus, plumeria, and columbine flowers, among others. Turns out that the number of petals flowering plants produce is a botanist’s province and a bit above my orchid-enthusiast paygrade. But here’s what I learned when I researched orchid petals.

Flowering plants fall into two main groups: monocots (short for monocotyledon) and dicots (short for dicotyledon or eudicotyledon). The seeds of monocots contain one plant embryo, while the seeds of dicots contain two embryos. Most monocots produce petals in multiples of three, and most dicots have either four or five petals. The arrangement is all about what’s most conducive to pollination.

Phalaenopsis labellum close-up.

So orchids would be dicots, right? Wrong. Three of an orchid’s petals of them are actually something else: sepals. Unlike petals, sepals are sterile. Orchids have two sepals on the side (lateral) and one at the top (dorsal). And the weird-looking petal in the middle, which encases the pollen cap, is called a labellum. The labellum is usually the most visually stunning petal and acts as a kind of insect runway.  Officially, that means orchids have three petals and three sepals (six altogether, rather than five) and are thus monocots. 

Credit: Dennis Chuah, via Wikimedia Commons.