Definition of "pissabed"

Of flowers there was no trace, save of the flowers that plant themselves, or never die […] The chief of these was the pissabed.

1953, Samuel Beckett, Watt, 1st American edition, New York, N.Y.: Grove Press, published 1959

The tufted hillock […] had no buildings on and only golden clumps of piss-the-bed that were not yet gone into misty balls of seed.

2016, Alan Moore, Jerusalem, Liveright, published 2016, page 139