Do conifer trees “flower?”

The answer, along with some tips for forecasting cone crops

Conifer trees are widespread across Minnesota’s northern forests.  The most common conifers of the northern forest include red pine, jack pine, balsam fir, white spruce, and black spruce.  Native tamarack is also a conifer, although it falls short of being an evergreen because it drops its needles in the fall.  Other, less common conifers in Minnesota’s northern forests, include Canadian yew, juniper, and hemlock.

All conifers are members of the Gymnosperm “Division” in the Plant Kingdom.  The word gymnosperm is Greek for “naked seed,” because the seeds of a conifer are not encapsulated in a fruit or nut – they are housed in woody cones and released / dropped when the cone opens.  Gymnosperms evolved long before their flower-producing cousins and were around during the time of the dinosaurs.  Conifers have truly survived the test of time.

Conifers produce flower-like structures in the early spring, but technically, no, they don’t produce true flowers.  Tree breeders and others in the business of plant reproduction sometimes refer to immature cones of conifers as “flowers” rather than the correct technical terms: strobilus, inflorescence, or immature cone.  When conifer seeds are released from a cone they don’t fall to the ground with a ‘thud’ like an acorn or a peach.  Instead, they glide in their helicopter-like seed coats, and may travel some distance before landing.  Conifers may lack flowers and most lack “fruit” but it’s worth noting that junipers produce small blue/grey berries that are an important food source for animals in the winter months.  Canadian yew produces a red-like berry that is actually a highly-evolved cone, not a fruit.  If you’ve ever purchased or cooked with pine nuts then you’ve eaten conifer seed!  Pine nuts are harvested from pine trees, mostly in Asia.  Red squirrels are notorious connoisseurs of Minnesota pine nuts, particularly those of red and jack pine.

Immature cones of conifer trees are short-lived structures that make a brief appearance during the months of May and June.  Male pollen cones are round structures that range from hot pink to deep purple.  As the pollen ripens and is released, the cones turn yellow and disintegrate.  They are most common on the lower half of the tree crown.  All conifers are wind-pollinated:  after being released from a pollen-producing cone, tree pollen travels on wind currents to its final destination.  Paternity studies have shown that pollen can travel hundreds of miles and produce viable seed.  That means a tree in Minnesota may have relatives in Ontario, Michigan or other distant areas.  A conifer tree standing in a field may look isolated, but there’s a high likelihood that the seed it produces was pollinated from either neighboring trees or trees from hundreds of miles away.  Isolation, in the Plant Kingdom, is relative to the distance that its pollen can travel.

Female cones are small cylindrical structures that range from hot pink to dark purple, and are most often found on the upper half of the tree crown.  During bumper cone years the female cones can be found all over the crown.  Female cones become “receptive” in the early spring, shortly after emerging from their winter bud.  Their scales remain open for a period of 5-10 days.  After pollination, their scales close, the cones become pendant, and they lignify to the more familiar dark brown “cone” structure.  In the late summer, spruce cones and second-year pine cones open and release seed.  White spruce usually open first, in mid-August followed shortly after by white pine, red pine, and jack pine.  Jack pine, especially in northeast Minnesota, may have “serotinous” cones that only open under intense heat.  The seed in a serotinous cone may remain viable for several years if the conditions are favorable.  In contrast, cones of balsam fir shatter, leaving no sign of the cones after shedding.

Dedicated cone collectors can begin planning their fall cone collections by making notes on the immature cone crop on native conifers in the late spring to early summer.  Pine cones (jack pine, white pine and Norway or red pine) require a second summer to fully ripen and mature, so check for the presence of “second-year” cones in the spring to gauge the potential for fall collection.  Cones that are shrunken, misshapen, dried out or stunted may have fallen victim to cone beetle, cone moth or a cone rust.  These cones will not produce viable seed and should be avoided during picking.  Sometimes damage from cone/seed insects and diseases isn’t visible until the late summer, so cones that looked fine in the spring might not produce viable spring in the fall.   Enjoy these fruits of the forest!

 

Carrie Pike directs the Minnesota Tree Improvement Cooperative, based at the University of Minnesota's Cloquet Forestry Center.

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1 Comment

  1. Looks like another heavy pine cone crop in the making this year in my woods, do some more site prep to allow seeds to reach mineral soil and become the new forest, natural regeneration with a tad bit of help.