A tale of two ferns
The hen and chickens fern (mouku or manamana) is a common New Zealand native fern. It had been observed that the cultivated hen and chickens fern grown and sold in garden centres around New Zealand looked different from the hen and chickens fern growing in the wild. Dr Leon Perrie and his colleagues set out to investigate why.
Two hen and chickens ferns
New Zealand has both wild and cultivated hen and chickens ferns. Dr Leon Perrie from Te Papa explains how to differentiate between the native plant and the hybrid.
Jargon alert: Dimorphism is the occurrence of 2 different forms of leaves on the same plant.
Point of interest: What differences did Leon find between the cultivated and the wild hen and chickens fern? What characteristic suggested it might be a hybrid?
Two hen and chickens ferns
Plants of the cultivated hen and chickens fern were known to look different from the wild plants. Most notably, the cultivated plants produced two sorts of fronds – fronds with narrow pinnae that made spores (fertile fronds) and fronds with wide pinnae that did not make spores (sterile fronds). Whole fronds could be entirely sterile or entirely fertile or have a mixture of sterile and fertile pinnae. This dimorphism of fronds was not seen in wild hen and chickens plants.
The spores of the cultivated hen and chickens ferns also looked different. Under a microscope, these spores were misshapen and hadn't formed properly. This further supported the idea that the cultivated plants were different from the wild plants. It also suggested that these plants were hybrids, as fern hybrids usually have abnormally formed spores.
A hybrid species
Frond dimorphism
The cultivated hen and chickens fern produces two sorts of fronds – fronds with narrow pinnae that make spores and fronds with wide pinnae that do not make spores. This dimorphism of fronds is not seen in wild hen and chickens ferns.
The search was now on to discover who the parents of the cultivated hen and chickens fern were. Leon knew that the cultivated hen and chickens fern produced ‘chickens’ (bulbils) just like the wild plants. This indicated that one of the parents of the cultivated plants was the wild-growing hen and chickens fern. But who was the other parent?
Leon and his colleagues first looked around for other candidates within the New Zealand fern flora. They looked closely at the morphology of ferns belonging to the Asplenium (spleenwort) group of ferns (the genus the hen and chickens fern belongs to), but they didn’t find a suitable candidate for the other parent in that group.
Fern hybrids
Dr Leon Perrie from Te Papa explains why they named the cultivated hen and chickens fern Asplenium x lucrosum. He explains why this fern hybrid can reproduce while most other fern hybrids cannot.
Point of interest:
Why does Leon say the hybrid hen and chickens fern has been profitable for the horticulture industry?
Why are most fern hybrids ‘dead ends’?
Then, while in the midst of a project sequencing the DNA of all of New Zealand’s Asplenium ferns, Leon included some DNA from the cultivated hen and chickens fern to see what that would tell him. Much to his surprise, the DNA from the cultivated hen and chickens fern didn’t match any of the other New Zealand species. Now he knew that the other parent, the missing parent, was not a New Zealand fern species.
To identify the other overseas parent, Leon and his colleague started looking close to home. They looked at ferns in Australia and its offshore islands. On Norfolk Island, they found a fern that had two forms. When it was not producing spores, the pinnae were very wide, and when it was producing spores, the pinnae were quite narrow. The fern is called Asplenium dimorphum, the ‘two-formed’ Asplenium. DNA from that plant matched DNA from the cultivated hen and chickens fern. This identified it as the second parent.
Hen and chickens fern
Hen and chickens ferns get their name from the little bulbils, the chickens, produced on the upper surface of the frond of the parent plant, the mother hen.
A new name for this species
The wild hen and chickens fern has the scientific name Asplenium bulbiferum. Once the cultivated hen and chickens fern was distinguished from the wild hen and chickens fern, it was given a new name, Asplenium x lucrosum. The ‘x’ denotes that this is a hybrid and ‘lucrosum’ is a Latin word meaning ‘profitable or gainful’. Leon chose this descriptor as a reflection of how profitable this particular hen and chickens fern has been for the horticultural industry.
Nature of science
Observation is a skill used by scientists. The fronds and spores of the cultivated hen and chickens fern differed from the native Asplenium bulbiferum species. This observation led the scientists to look more closely at the cultivated hen and chickens fern to determine its origins.
