Ferns — Various Families

Ferns are not flowering plants.  They lack the separate male and female structures that form the basis of most flowering plants’ reproductive processes.  Instead of using seeds, ferns make spores.  When spores fall on a suitably moist, shady place, they begin the fern’s reproductive cycle.  Because ferns need liquid water for a crucial reproductive step, ferns are not found in sunny, dry locations.   Fern structures have their own names:

  • A fern’s leaf is called a frond.  It is divided into pinnae, which are in turn subdivided into pinnules
  • The underside of the pinnules contain sori, which in turn contain sporangia, which produce the spores
  • Sori may be covered by a membrane-like indusium.  A false indusium is  a covering formed by a reflexed margin of the pinna / pinnule.  Not all ferns have clearly defined sori

All ferns included here are native to California.

Western Lady Fern – Athyrium filix-femina var. cyclosorum (Woodsiaceae: Cliff Fern family)

Frond:

25–130 cm

Pinnate:

1–2 ×

Pinnule:

Lobed /  toothed

Sori:

Round to J-shaped

Indusium:

Round to J-shaped

Notes:

This is easily mistaken for Wood Fern (Dryopteris arguta, see below).  However, its fronds are significantly larger and more broadly triangular, noticeably softer to the touch and generally paler in color.  The lower 2–4 pinnae are much shorter than those immediately above.  Sori may be round, oblong or J-shaped.  Indusia, if present, will be similarly shaped, attached on the inner side of the sori, often with hairy margins.  Found in meadows and streambanks.

Wood Fern – Dryopteris arguta (Dryopteridaceae: Wood Fern family)

Frond:

30–60 cm

Pinnate:

(1)2 ×

Pinnule:

Finely toothed

Sori:

Round

Indusium:

Yes

Notes:

This is the commonest evergreen fern to be found in oak woodlands, each plant producing several fronds from its base.  This differentiates it from Western Bracken Fern (Pteridium aquilinum, see below), which has a distinct stem with fronds branching  from it.  The fronds are lanceolate, but the pinnules tend to be rounded, with each vein ending in a spine-tipped tooth.  The sori are covered by a roundish or kidney-shaped indusium.  This could be confused with Lady Fern (Athyrium filix-femina, see above), but Wood Fern fronds feel a little tougher and firmer, and are less broadly triangular.

California Sword Fern – Polystichum californicum (Dryopteridaceae: Wood Fern family)

Frond:

40–100 cm

Pinnate:

1–2 ×

Pinnule:

Various

Sori:

Round

Indusium:

Yes, ciliate

Notes:

This is similar to Dudley’s Sword Fern (Polystichum dudleyi, see below) but with some subtle differences.  The base of the pinnules is clearly tapered and without lobes.  Multiple sori on each pinnule appear to be common.  Indusia, if present, are, as with Dudley’s Sword Fern, delicate and with hairy margins.  The fronds are much softer than Sword Fern (Polystichum munitum, see below).  This species is thought to be a sterile hybrid between P. munitum and P. dudleyi.

Dudley’s Sword Fern – Polystichum dudleyi (Dryopteridaceae: Wood Fern family)

Frond:

50–100 cm

Pinnate:

2 ×

Pinnule:

Various

Sori:

Round

Indusium:

Yes, ciliate

Notes:

This produces several arching fronds, softer to the touch than Sword Fern (Polystichum munitum, see below).  Pinnules are abruptly tapered at their base, often lobed and more or less divided or serrate or pinnately cut.  Indusia, if present, are delicate and with hairy margins.  Found in redwood and mixed evergreen forests.

Sword Fern – Polystichum munitum (Dryopteridaceae: Wood Fern family)

Frond:

60–140 cm

Pinnate:

1 ×

Pinnule:

Serrated

Sori:

Round

Indusium:

Yes, ciliate

Notes:

This is one of the most commonly found ferns, in oak woodland and, especially, in redwood forests. Each plant may produce many stiff, shiny, deep green fronds.  The slender pinnae have serrated margins. The broadened base of a pinna is said to resemble a sword’s hilt.  The axis of the frond (the “rachis”) has brown scales.  The sori are round. Like other Polystichum, indusia, if present, have marginal hairs and are “peltate”, i.e. with a stem attached to the lower surface like a parasol.

Western Bracken Fern – Pteridium aquilinum var. pubescens (Dennstaedtiaceae: Bracken family)

Frond:

< 1.5 m

Pinnate:

3 ×

Pinnule:

Entire

Sori:

Near margin

Indusium:

False

Notes:

The fronds are at first sight similar to those of Wood Fern (Dryopteris arguta, see above), but Bracken Fern has a distinct stem (typically about 1 m tall) with fronds branching off it; while the fronds of Wood Fern all arise directly from the fern’s base.  Also unlike Wood Fern, it is deciduous.  Sori are concentrated around the margins of the pinnules, more or less covered by the false indusium. This fern tends to prefer open areas where it can spread extensively.

Giant Chain Fern – Woodwardia fimbriata (Blechnaceae: Deer Fern family)

Frond:

1–2 m

Pinnate:

2 ×

Pinnule:

Serrated

Sori:

Oblong

Indusium:

Yes

Notes:

This is one of our largest ferns.  It favors damp conditions, and is generally found near streams or seeps.  The pinnae are clearly separated, and pinnules are pointed and very finely serrated.  The common name derives from the neat lines created by the oblong sori, and which are visible on both the upper and lower surfaces of each pinnule.  As the sporangia mature, the indusium opens lengthways like a lid, to reveal the sporangia underneath.