Epidendrum Pacific Rose Part 2: The Pollinator’s Story.
It can end in tears when small pollinators land on some species of Epidendrum orchids.
Pollination.
The flower has a quirky, inverted appearance. Unlike other orchids its lip sits above the petals. Botanists refer to this as a resupinate flower.
Three prominent lobes with serrated edges forming the orchid lip wave excitedly at you. The same warm greeting also attracts male Lepidoptera, who use the lip as a landing pad before clumsily searching for nectar in the flower tube. Insects continually pick up and drop off pollen. They struggle to reach into the small, narrow flower tube with its recessed stigma.
It can end in tears for the pollinator.
Craneflies and micro moths also approach these plants. They panic when their proboscis becomes glued to the inside of the flower tube and often struggle for hours before escaping. Sometimes, the struggle is futile.
A closer look.
Four oblate pollinia sit at the top of the column.
Epidendrum Pacific Rose is a hybrid, so I’m unsure whether it produces nectar. Pollinators are undeterred, however, and quickly spot the presence of a cuniculus, a putative nectar-producing organ, protruding tantalisingly from the stigmatic cavity.
The Cuniculus
The cuniculus at the entrance to the stigmatic cavity is a narrow tube with a narrower opening at its tip.
The cuniculus originates in a space beside the ovaries. It is formed by fusion of the basal part of the labellum (or lip) with the column. It extends past the ovary and follows the transmitting tract before exiting the flower tube in full view of pollinators.
The flower from a different angle.
There is only just enough room for large male butterflies and moths to perch on the lip. The flower tunnel is far too small to go any further. The insect has to use its proboscis to probe around inside the flower.
Darwin was the first to speculate that Epidendrum flowers were ideally suited to pollination by Lepidoptera. Pollinaria should glue to the insect proboscides while they are rummaging around at the entrance to the flower tube. (See reference at the end of this article).
Reference.
Insects pictured using their proboscis’ to probe inside the flower tube:
Pollination in Epidendrum Densiflorum hook.
Silveira RS, Singer RB, Ferro VG. Pollination in Epidendrum densiflorumHook. (Orchidaceae: Laeliinae): Fraudulent Trap-Flowers, Self-Incompatibility, and a Possible New Type of Mimicry. Plants (Basel). 2023 Feb 3;12(3):679. doi: 10.3390/plants12030679. PMID: 3677176I4; PMCID: PMC9921780.