Sunday, 25 June 2017

Apium repens

There is a small perennial plant, Apium repens (creeping marshwort) which is only known to be recently found at two sites in the UK – Port Meadow in Oxford and our very own, Walthamstow Marsh.

In 2002, botanist Brian Wurzell found young plants of Apium repens in the ditches on Walthamstow Marsh.
Young plants of Apium repens found by Brian Wurzell in a new ditch in Walthamstow Marshes, in 2002.
The plants flowered with the characteristic long peduncle and bracts of Apium repens. It was later confirmed that the plants were very similar to the forms on Port Meadow. In 2003 cattle were re-introduced on Walthamstow Marshes to maintain the open conditions the plant requires. In the summer of 2004 A. repens had hundreds of inflorescences.

Fast forward to Walthamstow 2017 and how fares the rarest of UK plants on the marshes?

Answer = to be confirmed.

There are two small patches of an Apium species on Walthamstow Marshes surrounded by marker stones, presumably at the place of the 2002 repens discovery, one bigger than the other.

Larger specimen on the left, smaller on the right.

Photos from May 2017.

There are also many other patches of Apium in the surrounding ditch and Bomb Crater Pond:

Photos from May 2017

Here’s where it gets interesting (frustrating). Apium repens has a close relative, Apium nodiflorum (AKA fools water cress), which it closely resembles and also hybridises with, forming the hybrid, A. x longipedunculatum.

In the above May 2017 photos, the leaflets are a little longer than wide, a feature of Apium nodiflorum. Apium repens has more or less orbicular leaflets, and has up to 6 pairs of leaflets.

All would become clear when it flowers in the summer.

Fast forward to summer… and sadly, it’s Apium nodiflorum all round so far.

For a positive Apium repens id, you are looking for something with leaves about as long as wide, with a flower stalk much longer than the stalks supporting the individual rays, and with bracts at the point where the peduncle divides to form the rays. It also roots at all the nodes.

The biggest stone circle patch has short peduncles and no bracts at the point where the peduncle divides to form the rays. The smaller stone circle Apium is not currently flowering.

Short peduncles and an absence of bracts are equally apparent with the numerous other Apium patches on the marshes:

So what does Apium repens actually look like?

The following annotated photo and sketch are good examples:

LNHS Recorder and Forensic Botanist, Mark Spencer, photographed a patch of Apium repens on the marshes in September 2016. So, hopefully it is still there, somewhere.

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