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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

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

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.

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.

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.

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