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Short Notes on Nature Singapore

2 March 2014 | Fern | Cyclosorus subpubescens |

The leaf of a fern is called frond. Fertile frond bears spores on their underside which is probably why it is considered different from a leaf and thereby given a different name. It follows that the parts on a frond are also given different names compared to the terms used for leaf.

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Most ferns do not have a visible stem. The frond appeared to emerge out from the ground and it is usually larger than a typical leaf. Rachis is the midrib of a frond while costa is the midrib of pinna (leaflet). What most people thought to be fern leaves is actually the pinna, part of the frond.

The fern pictures used in this illustration was from Cyclosorus subpubescens, an uncommon fern that may be confused with the very common Giant Sword Fern (Nephrolepis biserrata).

The sori (spore-bearing bodies) of Cyclosorus subpubescens were arranged in parallel rows on the underside of fertile fronds. Features of sori and their arrangement patterns were helpful in the identification of ferns. Young sori were white in colour and they gradually turned to dark brown colour as they matured.

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photo Up till the mid of this month, I had named this fern as Cyclosorus heterocarpus, another lookalike fern that I had yet to determine whether it was present in Singapore. The breakthrough came about when I was examining the pictures of the 2 ferns in the Ferns of Thailand, Laos and Cambodia website. The most distinctive clue came from the faint line that run along the length of the fiddle head of Cyclosorus subpubescens. This feature is not present on the fiddle head of Cyclosorus heterocarpus shown in the website. A fiddle head or crosier is the emerging young frond presented in a coiled pattern.

I checked my pictures taken before 2014 and no picture of the fiddle head was available. I went to the field last weekend to find the fiddle head of this fern but only managed to find one which had a few small leaflet on it. Despite the not-so-ideal picture, I did find the line along the fiddle head when I enlarge the picture back home. Hence, I was quite certain that I had got the name right this time round.

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