# Mackay's Fragile Fern (*cystopteris tenuis*)

Mackay's Fragile Fern (Cystopteris tenuis) is a delicate and resilient perennial fern native to the rocky woodlands and cliffs of eastern North America. Named after the botanist A.H. Mackay, this species belongs to the fragile fern genus, characterized by its slender, easily broken stems and highly dissected, lace-like fronds. Unlike many other ferns that require deep, moist soils, this species thrives in crevices of rocky outcrops, cliffs, and talus slopes, where it anchors its short, creeping rhizomes. It is highly valued by native plant enthusiasts for its elegant appearance and ability to colonize challenging, shaded stone environments.

- **Category:** [Plants](https://www.snappit.app/explore/categories/plant)
- **Rarity:** Common
- **Danger:** 1/5 · Very low
- **Snaps:** 1
- **Habitat:** Typically found in shaded rocky woods, moist cliffs, talus slopes, and limestone ledges.

![Mackay's Fragile Fern](https://inaturalist-open-data.s3.amazonaws.com/photos/262311966/medium.jpg)

Photo: Choess, CC BY-SA 4.0 · [iNaturalist](https://www.inaturalist.org/photos/262311966)

## Appearance

This small-to-medium fern features delicate, light-green, bipinnate to pinnate-pinnatifid fronds that typically reach 10 to 40 centimeters in height. The fronds are lance-shaped and taper toward both ends, growing from a short, creeping rhizome. Its stem (stipe) is very slender, smooth, and fragile, showing a reddish-brown to straw-colored base. Underneath the pinnules, circular spore-producing structures called sori are partially covered by hood-like indusia, which shrivel and peel back as the spores mature in mid-to-late summer.

## Taxonomy

- **Kingdom:** Plantae
- **Phylum:** Tracheophyta
- **Class:** Polypodiopsida
- **Order:** Polypodiales
- **Family:** Cystopteridaceae
- **Genus:** Cystopteris

## Interesting facts

- Despite its common name 'fragile fern', this plant is incredibly tough, often growing directly out of sheer rock walls where few other plants can survive.
- Its species name 'tenuis' is Latin for 'thin' or 'slender', referring to the delicate, paper-thin texture of its leaflets.
- Unlike many larger ferns, Mackay's Fragile Fern is known to go dormant and wither during dry midsummer heat waves, only to resurrect with fresh green fronds when autumn rains arrive.

## Special abilities

- **Epilithic Colonization:** Capable of anchoring its root-like rhizomes directly into narrow rock crevices and pockets of shallow soil on vertical cliff faces.
- **Estivation Sprouting:** Can senesce (die back) during dry mid-summer spells and rapidly produce a fresh flush of new fronds when moisture returns in autumn.
- **Active Spore Catapulting:** Utilizes a specialized ring of cells (the annulus) on its sporangia that dries and snaps forward, forcefully launching microscopic spores into passing wind currents.

## Measurements & details

- **Length:** 10-40 cm
- **Weight:** 0.01-0.05 kg
- **Lifespan:** 5-15 years

## Diet & Feeding

As a photosynthetic plant, Mackay's Fragile Fern synthesizes its own energy from sunlight, carbon dioxide, and water while absorbing key mineral nutrients through its roots.

- **Primary Foods:** Sunlight, Water, Carbon Dioxide, Soil Minerals

## Ecological connections

- **Parasite:** Fern Rust Fungus (*Hyalopsora polypodii*) — A specialized rust fungus that infects the fronds, utilizing the fern as a host to complete its lifecycle.
- **Eaten by:** [White-tailed Deer](https://www.snappit.app/explore/white-tailed-deer) (*Odocoileus virginianus*) — An herbivorous mammal that occasionally grazes on the delicate fronds in rocky, forested areas, especially in early spring.
- **Competitor:** Anomodon Moss (*Anomodon attenuatus*) — A shade-loving moss that often grows alongside this fern in moist rock crevices, competing for space and water.

## Safety

**Danger:** 1/5 · Very low

No special safety notes yet.

## Frequently Asked Questions

### How to identify Mackay's Fragile Fern?

Compare frond shape, how the leaflets are arranged, the stalk, and any spore clusters you can see. A single detached leaflet often hides the plant's overall growth pattern. Fern Identifier: upload a photo and compare the visible details.

### How long is Mackay's Fragile Fern?

10-40 cm

### How much does Mackay's Fragile Fern weigh?

0.01-0.05 kg

### How long does Mackay's Fragile Fern live?

5-15 years

### What does Mackay's Fragile Fern eat?

As a photosynthetic plant, Mackay's Fragile Fern synthesizes its own energy from sunlight, carbon dioxide, and water while absorbing key mineral nutrients through its roots.

### Where is Mackay's Fragile Fern usually found?

Typically found in shaded rocky woods, moist cliffs, talus slopes, and limestone ledges.

## Where to spot

- [Bartholomew's Cobble](https://www.snappit.app/guides/places/bartholomews-cobble) — Massachusetts, US · Nature Reserve
- [Palisades State Park](https://www.snappit.app/guides/places/palisades-state-park) — South Dakota, US · State Park

## More Plants

- [white snakeroot](https://www.snappit.app/explore/white-snakeroot) (*Ageratina altissima*)
- [tree-of-heaven](https://www.snappit.app/explore/tree-of-heaven) (*Ailanthus altissima*)
- [western sword fern](https://www.snappit.app/explore/western-sword-fern) (*Polystichum munitum*)
- [common milkweed](https://www.snappit.app/explore/common-milkweed) (*Asclepias syriaca*)

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Source: [Mackay's Fragile Fern: Facts & Places to See — Snappit](https://www.snappit.app/explore/mackays-fragile-fern)