Seed Dispersal Fascination

Walking through the winter garden today, I wandered among patches of brown, spent perennials and annuals long gone to seed. I let the seeds linger for the sake of wintering birds in need of food and to hopefully let them spread their habit a little.

Frostweed (Verbesina virginica L.)

Frostweed (Verbesina virginica L.)

I’ve always been fascinated by seeds — shape, size, patterns, and especially dispersal methods. Plant species over all their thousands to millions of years of existence have evolved remarkable ways to disperse their seeds. After all, it’s to their advantage to send forth their seeds, not just to ensure population survival but to also not have tons of little baby plants growing up at their feet, so to speak — stealing sunlight, water, nutrients, and space from their parents.

Frostweed (Verbesina virginica L.) produces copious seeds to feed overwintering birds.

Frostweed (Verbesina virginica L.) produces copious seeds to feed overwintering birds.

Different plant species have different means of getting their seeds out into the world, of course, but generally speaking they fall into several main dispersal categories:

  • Wind (Seeds float or flutter with help of the wind)
  • Expulsion (Seeds are forcibly expelled)
  • Gravity (Seeds bounce and roll)
  • Animals (Seeds stick to, are eaten and digested by, are eaten as fruits with seeds discarded, or are stored and planted by animals. Note that humans take seed dispersal to a whole other level — sometimes with disastrous effects, such as spread of invasive plants.)
  • Water (Seeds float to a new location)
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Assorted cones

Furthermore, some plants only release their seeds in response to certain triggers, such as heat from the sun, water, or drying. As another example, certain pine trees might drop their cones all over a woodland floor, but the cones will only release the actual seeds in response to a fire hot enough to burn living trees in the area. Such a trigger-dependent adaptation is called serotiny.

Wafer Ash (Ptelea trifoliata) seeds have circular "wings" to help them flutter to the ground.

Wafer Ash (Ptelea trifoliata) seeds have circular “wings” to help them flutter to the ground.

Some seeds have parachute-like adaptations, such as the classic dandelion, that let them travel long distances on the wind, while other seeds have “wings” that help them flutter down or reach several feet away. Other seed heads spill out their seeds when a strong wind tilts the stem, such as the seed cup of a poppy.

My favorite example of expulsion, or forced dispersal, is that of the bluebonnet, whose pods twist and pop open in the warm sun, sending out their pebble-like seeds out a few feet away. Unfortunately, I don’t have any pictures of this action… yet!

For water dispersal, think of seeds that float, such as those of water lilies, lotus, and the all-time classic… coconuts.

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Cedar waxwings feasting on Yaupon (Ilex vomitoria) berries

In terms of animal dispersal, I can attest, having three dogs, that seeds that have hooks, spines, or barbs (such as burrs and stick tights) are very effective in getting their potential offspring spread far away from the parents. Birds can carry seeds great distances simply by eating fruits and seeds off one plant and then pooping out the seeds many feet or many miles away. And then there are squirrels and blue jays, notorious for planting acorns and other tree seeds, some of which will surely grow.

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The seeds of Inland Sea Oats (Chasmanthium latifolium) present themselves in a graceful arch, until birds and wind start to disperse the seeds.

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As the seedheads of Velvet-leaf Mallow (Allowissadula holosericea) mature, they open to reveal a cool radial pattern.

Gravity comes into play with many species — obviously it’s going to influence where seeds land, regardless of overall dispersal method. Never underestimate the success potential of a seed that has simply dropped and rolled to a perfect soil and light location.

seedmaterials11-15Working with kids has made the study of seed dispersal all the more fun. Want to challenge your children or students? Have them use different craft materials to design their own seeds with different methods of dispersal. Then test their dispersal success — possibly with a fan, a tub of water, a measuring tape to determine expulsion distance, or cloth or stuffed animal as “fur.” Try it yourself, too!

Caterpillar Hotel

This weekend I taught all about creating habitats at a conference for kids. As part of the presentation, I brought along this little guy — one of our black swallowtail caterpillars.

swallowtailcat06-13-10.jpgTalk about a wonderful assistant — not only did he delight the families in the workshops, but he and I visited with a lot of people as I carried him around during the rest of the conference. It was simply too hot in the car for me to leave him in there, so he got to walk around with me, happily munching on dill set in a bouquet of native TX flowers.

When I got home, I let him go back to his world of giant dill in my backyard. Later I walked around to check on my other caterpillars and to look for more. I’m thrilled to have found our first Gulf Fritillary caterpillar on our Passionvine.
gulffritillarycat06-14-10.jpgBut when I went to check on the new bird poop caterpillars I’d found the day before on my Wafer Ash, I saw with alarm a hornet visiting the leaves of the tree, hunting the same way they hunt the caterpillars on my milkweed. I was relieved to find two of my caterpillars were happily munching on the citrus leaves.

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And to my delight, I found lots of eggs all over the tree. Here’s a caterpillar with a few eggs nearby.

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But to my horror, my third little caterpillar was dead. My first thought was that a hornet had killed it, but this was a false accusation, because on closer inspection it was clear that my little caterpillar was being feasted upon by two bugs I didn’t recognize. It turns out that they are predatory stink bugs. Predatory stink bugs? I’d never heard of such a thing. And what — they are considered beneficial bugs in the garden, so I can’t get rid of them? I have to just let these stink bugs feast on my caterpillars? Now THAT stinks! I thought having to accept hornets and wasps going after my caterpillars was bad enough. Thinking about it, I saw somewhat similar bugs over on my dill a few days ago. I think I know what’s been contributing to the deaths of some of my swallowtail caterpillars.

predatorystinkbugs06-13-10.jpgWell, I couldn’t bear it the thought of more giant swallowtails falling prey to the terrible sucking tubes of these clearly ferocious predators, so I decided that my remaining caterpillars earned deluxe accommodations in our Caterpillar Hotel, a collapsible laundry basket that has soft, breathable fabric on the sides. It’s perfect, and we’ve had great success so far, with 3 caterpillars going to chrysalis stage. I’ve released one beautiful butterfly already — here it is, a Black Swallowtail just before release.

blackswallowtail06-13-10.jpgSo I gathered dill and wafer ash for the two caterpillar species and put the plants in a bottle of water. Then I collected my caterpillar assistant and my two adorable bird poop caterpillars. Isn’t it a lovely Caterpillar Bouquet?

caterpillarbouquet06-13-10.jpgBouquet in the hotel:

caterpillarhotel06-13-10.jpgYesterday I wasn’t worried about the Gulf Fritillary (he’s on the other side of the yard), but today I’m having second thoughts and might be checking him into the Caterpillar Hotel as well.

I know I can’t rescue all my caterpillars — nature must take its course — but here and there I don’t mind lending them a helping hand.

It might be time to set out a new banana to distract the hornets and wasps, as well. I’ll add a rotting one for the butterflies — they love it so. HOLD ON — BRILLIANT IDEA — I’ll move the predatory stink bugs to my tomatoes and let them do their thing on my true pest bugs! By Jove, I think she’s got it!

Speaking of butterflies, a new species has entered the garden. Bordered Patch — what a beauty! Unfortunately, my pup scared it off after I grabbed only a couple of shots.

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borderedpatchb06-13-10.jpgOver on the dill, this damselfly let it all hang out, wings included.

damselfly06-13-10.jpgThe dill is going to seed. I think it’s still pretty, even when brown. There’s plenty of dill left for the swallowtails, though.

dillseed06-14-10.jpgThe Cinnamon Sunflower is reaching toward the sky — now officially taller than its neighbor, the Mexican Redbud tree. I hope the tree doesn’t get a complex. Looks like a couple of buds are forming — I can’t wait! The giant sunflowers by the house are still struggling, poor things.

cinnsun06-14-10.jpgAnd the pretty Flame Acanthus blooms are flashing red from behind the wispy Big Muhly.

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We finally got Mr. Vulture moved — now he looks down on us from our chimney, as he was always meant to do.

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He can stand guard over the Caterpillar Hotel.

Whatnots

I just couldn’t come with a title for this one. But I had fun taking photos!

The Cinnamon Sunflower is about 3 feet tall now, but still no blooms. Looking pretty snazzy even without the blooms, I must say.

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I never realized how fun milkweed seeds are, fresh from a pod. Hopefully some of these will germinate — I need more milkweed!

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Still damp from a gentle rain, the Passionvine is happily entwining along its trellis. With luck it will hide our A/C unit soon, at least until the caterpillars start munching!

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Passiflora flowers just might be the most bizarre flowers out there. I mean seriously — how on earth did nature come up with that crazy design?

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The tripod of a stigma at the top looks like some alien straight from a sci-fi movie.

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The coneflowers are huge and teasing me with blooms to come.

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I’m not sure whether it was the rain or the change in temperature, but I finally got a Checkered White butterfly to hold still for a photo.

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And a Dainty Sulphur — both of these butterflies usually tend to dart around like mad if I get too close. Gotcha, little flutterbies!

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I’ve been noticing more wasps visiting the dill lately, and the caterpillar deaths have increased, so I decided it was time to create a butterfly tent. Within a day we had our first swallowtail chrysalis. The tent is a collapsible $9 laundry hamper — much cheaper and much larger than the “butterfly kits” you can buy online and in various stores.

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Okay, what’s this bug? Good guy? Bad guy? Found him on my native White Honeysuckle bush. I guess I could go look him up.

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In other news, I found little slimy larval stuff eating one of my tomato leaves. I took a picture, but they’re gross and I decided that they messed with my pretty zen pictures, so I’m not posting it today. The slimy things are in the compost bin now. I don’t know whether they’re good guys or bad guys, but they were working as a team and my gut told me I didn’t want more of them around. And there was a leaf-footed bug on another tomato leaf. Little booger got away. Gah. But at least I’m onto him.