Listen to Nature Almanac
on KGNU Radio,
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Fri, April 4, 2008, 8:06 a.m.

Boulder Weather

Avg. High:  61° F
Avg. Low:  35° F

Max. High: 88° F (1989)
Min. Low: -3° F (1975)

Avg. Precip: 2.54"
Max. Precip: 9.18" (1900)

Avg. Snow: 9.0"
Max. Snow: 44" (1957)

Max. Wind: 127 mph (1982)

April Wildflowers

Sand Lily
Leucocrinum montanum

Nuttall's Violet
Viola nuttallii

Chiming Bells
Mertensia lanceolata

Bell’s Twinpod, a mustard endemic to Larimer, Boulder, and Jefferson counties, blooms on shale outcrops along US 36  in mid-April.

People sometimes ask what's the "rarest" plant in Boulder County. One choice would be White Adder’s-Mouth (Malaxis monophyllos), a tiny orchid that grows in one or two small seeps on Green Mountain and has been found nowhere else in Colorado. But a case could be made for Bell’s Twinpod (Physaria bellii). Though locally common, this tenacious mustard is globally very rare, growing only on limestones and calcareous shales in the northern Front Range foothills.

In mid-April the mustard's bright yellow, wheel-shaped florettes stand out against the dark shales on either side of US 36 north of Boulder. Bell’s Twinpod is named for its inflated, two-chambered seed pods. "Physa" means bellows. The flower stalks splay out around a central cluster of pale green, fiddle-shaped leaves.

Because it grows only on bare shales in a minute geographic area, this mustard is particularly vulnerable to environmental change. In an article for the Boulder Daily Camera, University of Colorado ecologist Jeffry Mitton reminds us that the nearly competitor-free niche that Bell's Twinpod has carved out is a precarious one. Shales erode rapidly, and this habitat specialist may survive only so long as the unique shale formations it has colonized persist.

Listen to the April 2008 Nature Almanac broadcast.

Other April Events

• Beaver, Raccoon, and Porcupine young are born.
• A few Burrowing Owls return and mate. Fragmentation and disturbance of prairie dog colonies, collisions with automobiles, and predation by urban-adapted carnivores have nearly driven this little owl from Boulder County.
• Prairie Falcons and Peregrine Falcons lay their eggs on cliff ledges in the foothills.
• Broad-tailed Hummingbirds return from Mexico and Central America, Swainson's Hawks from Argentina.
• Bullsnake males joust, cobra-like, to win the opportunity to mate with nearby females.

April 2008 Events

April 20: The full moon rises at 8:29 p.m.

• Ice Breaking in the River (Arapaho)
• Green Grass (Pawnee)
• When the Geese Lay Their Eggs (Cheyenne)

April 22: The Lyrid Meteor Shower peaks shortly after sunset. Up to 20 meteors per hour may be visible once the quarter moon sets around midnight.

Photo credits: Flowers and Burrowing Owls - Stephen Jones
Falcons (link) - Bill Schmoker

Read Ruth Carol Cushman and Stephen Jones's Nature Almanac column in the Daily Camera "Get Out" section the first Friday of each month.

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