Onoclea sensibilis var. interrupta

Sensitive Fern Onocleaceae

A distinctive and rather uncommon form of the Sensitive Fern, Onoclea sensibilis var. interrupta is best understood in relation to the typical species, from which it differs in both the architecture of its fronds and its overall habit. While Onoclea sensibilis is usually encountered as a strongly spreading fern with broad, evenly pinnatifid sterile fronds, this variety shows a noticeably more irregular, “broken” or interrupted frond structure, from which its name is derived.

In the type species, the sterile fronds are broadly triangular, soft green, and evenly divided into pinnae that give a lacy but consistent appearance. In var. interrupta, however, the pinnae are more irregularly spaced and often appear unevenly developed along the rachis, giving the frond a slightly disjointed or segmented look. This creates a lighter, more open texture in the foliage, and the plant as a whole can appear less lush but more finely detailed.

The fertile fronds are produced in the same manner as in the type species—erect, bead-like and dark brown at maturity—but may be somewhat less numerous depending on growing conditions. As with all forms of O. sensibilis, these fertile structures persist well into winter, providing architectural interest after the sterile fronds have collapsed with frost.

Ecologically and culturally, var. interrupta shares the same preferences as the typical form: it thrives in consistently moist to wet, humus-rich soils, particularly in shaded or semi-shaded positions. It is equally capable of spreading via creeping rhizomes, though some growers report it to be marginally less vigorous than the standard species, possibly due to its more finely divided foliage.

The key distinction for gardeners lies in its texture and visual rhythm. Where the type species offers bold, continuous fronds and a strong colonising presence, var. interrupta provides a more delicate, interrupted patterning that can be especially effective in detailed woodland plantings or fern collections where subtle morphological variation is appreciated.

Garden use: Best suited to shaded, moisture-retentive woodland gardens, fern collections, and naturalistic plantings where its finer, more irregular frond structure can be observed at close range.

Hardiness: H5 (-15 to -10°C)
Height: 30–100 cm
Spread: Spreading via rhizomes, potentially forming colonies
Seasonal interest: Spring to autumn (sterile fronds), winter (persistent fertile fronds)