Adiantum tenerum
[Brittle Maidenhair Fern]

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Online Resources: | Flora of North America | Backyard Nature | Plants of Saint Lucia |

I named this fern as Adiantum tenerum when I first obtained its picture back in 2008. Later, I noted that the name Adiantum tenerum was not listed in the Singapore flora checklist published in 2009 [1] while the name Adiantum raddianum was listed. As both ferns look very similar, I decided that it was more likely to be an Adiantum raddianum.

In November 2014, I received a note to re-check the name of this fern versus my pictures. Apparently, in Adiantum tenerum, the base of the segment stalk that connect to the base of the pinnule should terminate in cupulelike swelling. A cupule is a tiny cup. I tried to look for the "cupulelike swelling" in my existing pictures. But, due to the smallness of the stalk, I could not tell whether there was a cup-liked base (see pictures below).

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In the same month, I went to take more pictures of the fern, hoping to confirm its identity. Though the new pictures (below) were slightly better, they were still not good enough to view such tiny feature. I could see vaguely the tiny cup-like end of the leaf stalk but it was not obvious in other pictures taken from the same plant.

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Then, I read this description of the sori (a structure that housed the spore-bearing bodies) of Adiantum raddianum from PIER website: "more or less orbicular-reniform". The round kidney-shaped sori is clearly illustrated in a picture from the Flora of Zimbabwe website. As for Adiantum tenerum, the indusium (a membrane that protect the sorus) was described as "transversely oblong to crescent-shaped" from the Flora of North America website. Looking at the shape of the indusia of the fern in my pictures, it should be Adiantum tenerum.

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Thereafter in the same month, I found the real Adiantum raddianum while visiting the Cloud Forest at the Gardens by the Bay.

Reference:

[1] Chong, K. Y., H. T. W. Tan & R. T. Corlett, 2009. A Checklist of the Total Vascular Plant Flora of Singapore: Native, Naturalised and Cultivated Species. Raffles Museum of Biodiversity Research, National University of Singapore, Singapore. Uploaded 12 Nov.2009. | Read article |