knotweeds

genus Polygonum

Member of knotweed family (family Polygonaceae)
dicots (class Magnoliopsida)
flowering plants (subphylum Angiospermae)

Except for old historical records and extremely rare examples that I don't expect to encounter, there are no other wild species of this genus in the bay area.

prostrate knotweed
Polygonum aviculare

stem 8–16 ribbed
a complex of mostly self-propagating plants with many sympatric and intergrading forms

oval leaf knotweed
Polygonum arenastrum

included here since iNaturalist includes purported local observations
I can find no description of how this is different from prostrate knotweed (Polygonum aviculare)
many sources consider this to be a subspecies/variety of prostrate knotweed (Polygonum aviculare)

beach knotweed
Polygonum paronychia

stem ± angled, ribs 0 or obscure

1 observed taxon / 2 unobserved taxons / 1 key

Chris’s observations: 3 (none are research grade)

Locations:

Sierra Vista OSP: 2
Coal Creek OSP

Months:

May: 2
Jun.: 0
Jul.: 0
Aug.: 0
Sep.: 1

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Taxon info: iNaturalist – Calflora – Jepson eFlora – FNA

Bay Area species: iNaturalist – Calflora