Botanizing in Alaska: Alpine Blueberry

The Alpine Blueberry (Vaccinium uliginosum) grows throughout Alaska. I took this photo during midsummer. The berries ripen during fall, so I didn't get any on the trip when I took the photo.

The ripe berries are well-regarded by humans and bears alike. Both can be found collecting them along roadsides in the fall. Ideally not in the same place at the same time, but you have to keep aware of your surroundings while berry picking in case you're lucky/unlucky.

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On a more recent trip than when I took this photo, I was lucky enough to find plenty of ripe blueberries to pick as well as a black bear filling itself on blueberries. I was especially lucky in that the two of us were picking berries in different places.

Within each berry are several tiny seeds. The seeds need a period of cold moist stratification before they will germinate effectively. I'll be planting a batch of seeds in a pot outside to see if I can get any plants to grow next year.

References:

• Bog/Alpine blueberry:
• https://www.flora.dempstercountry.org/0.Site.Folder/Species.Program/Species.php?species_id=Vacci.uli
• http://plants.alaska.gov/pdf/Blueberry.pdf

Botanizing in Alaska: Black Spruce

Black spruce (Picea mariana) are a common forest tree up in central Alaska, ranging north until the tundra. The trees in the image at left are in Fairbanks, Alaska.

The trees grow slowly, eventually topping out at 20 meters in the southern parts of their range. The trees in Fairbanks are generally much shorter. The trees here are maybe 30 ft tall, growing less than a foot apart. They can get away with such crowding because those two trees are probably separate trunks growing from a unified root system. Large connecting roots grow horizontally just under the surface and graft together with their neighbors. The individual trunks share nutrients and carbohydrates and thus don't suffer from competitive shading as much as trees that don't cooperate in this manner.

This style of growth also potentially helps them stay upright in the swampy soils they're usually found in. The horizontal grafted root structure spans wider than the cluster of trunks, allowing the cluster to stay upright even if the ground beneath part of the cluster can't support their weight. This style of growth would help them grow horizontally out onto a bog, with some trees suspended over the lake hidden below.

References:

• Black spruce: https://www.oecd-ilibrary.org/docserver/9789264095434-10-en.pdf?expires=1571892005&id=id&accname=guest&checksum=D3380DF0E335EC3E021633EB1523689A
• Root grafts:
• https://www.nrcresearchpress.com/doi/pdf/10.1139/cjfr-2016-0121
• https://www.sciencedaily.com/releases/2011/06/110608141529.htm

Botanizing in Alaska: Low-Bush Cranberry

I still have some photos from my last trip up to central Alaska to go through. I found this plant on a drive in the vicinity of Fairbanks-AK. We drove up a mountain until we were at the tree-line. While walking around, we saw lots of this plant woven through thick mats of moss and other small plants. Though it didn't have any berries yet, I was able to find a few flowers.

Called Lingonberry or Low-Bush Cranberry (Vaccinium vitis-idaea), this plant has a circumpolar distribution. It is prominent in Scandinavian cuisine and is one of the plants I fondly remember from my childhood in Anchorage-AK. I was hoping to find a small specimen I could transplant to grow in Minnesota. The plants I found, however, spread over several feet wide (though most was hidden in the thick moss). I haven't found any research into how long the plants can live, but these were undoubtedly many years old. I didn't take any cuttings or plant samples, as doing so would have been too disruptive to the fragile plant community.


References:

• en.wikipedia.org/wiki/Vaccinium_vitis-idaea
• www.alaska.org/advice/low-bush-cranberry
• www.adn.com/food-drink/article/alaskas-rugged-low-bush-cranberries-turn-out-be-antioxidant-superstars/2013/11/26/
• www.uaf.edu/files/ces/publications-db/catalog/hec/FNH-00110.pdf

Botanizing in Alaska: Northern Bluebells

1. Mertensia paniculata.

Around the house we were staying at in central Alaska, the woods were full of this lovely blue-bell flower (fig 1). The name we knew for the plant was Comfrey (Symphytum officinale).

2. Symphytum officinale.

At the Fairbanks University botanical garden, we found a plant labeled as Comfrey (fig 2) that looked quite distinct from the plants in the woods. With its larger and more purple flowers, we thought it was strange. We interpreted the differences as being related to the plants being from different varieties. Many domesticated versions of flowers look distinct from their wild relatives, after all.

Looking through a list of Alaska native flowers, I found our blue flowered friend. It is named Mertensia paniculata ("Northern Bluebells" or "Chiming Bells") and grows as a woodland wildflower throughout central Alaska. The flowers and overall growth form of the two species are remarkably similar for not being in the same genus. The two genera are in in the same family, the Boraginaceae, so the similarities make some sense in the end.

I did succeed in collecting seeds for M. paniculata, so I might be able to get further pictures of the species later this season.


References:

• M. paniculata
• en.wikipedia.org/wiki/Mertensia_paniculata
• S. officinale
• en.wikipedia.org/wiki/Comfrey
• en.wikipedia.org/wiki/Symphytum_officinale
• www.turtlepuddle.org/alaskan/wild/flowers-2.html 
• en.wikipedia.org/wiki/Boraginaceae

Botanizing in Alaska: Labrador Tea

Labrador Tea is the common name for a few related species in the Rhododendron genus. In central Alaska I found specimens of R. tomentosum growing through foot-thick moss growths high on a mountain near the tree-line. Like most species in the genus, it produces lovely flowers.

The plants produce a range of interesting phytochemicals that have long been used by native communities. The interesting ethnobotanical history of the plant (as well as personal descriptions of its use in a tea from my wife), made me interested in collecting seeds or a live specimen of the plant for a more detailed ongoing examination.

On this trip, I learned that what can look like a small herbaceous plant can really be the tip of one branch of a very wide- and low-growing shrub. This makes it much harder to collect a live specimen without disrupting a large area of other potentially delicate plants. I chose not to do this. I also learned that the summer solstice is not the appropriate time of year to collect seeds from this species. The plants weren't in flower or even developing flower buds yet.

My next trip to the area will have to be during the local berry season in late autumn. Berry season in central Alaska means lots of interesting and diverse berries to taste, as well as a straightforward means to collect seeds from the plants that produce them.


References:

• en.wikipedia.org/wiki/Labrador_tea
• en.wikipedia.org/wiki/Rhododendron
• en.wikipedia.org/wiki/Rhododendron_tomentosum
• www.pbase.com/holopain/image/18027321 
• www.ncbi.nlm.nih.gov/pubmed/23352748 

Botanizing in Alaska: Bunchberry

This marks my 100th blog post. I started this blog to provide an outlet for my desire to write and share some of my photography and thoughts/observations about biology. It was intended to be an outlet that didn't come with the pressures of the academic work life I had then. I was a professional research biologist (with a heavy computational specialty) and for now am out of academia and living the life of an office grunt.

My day job doesn't really have much to do with the study/application of biology, but there is little that could keep me from considering myself a biologist. Often times, the biology think about relates to my garden, but I wouldn't consider this to be a gardening blog. It is more that I consider my garden to be part of my "research lab".

My garden allows me to do certain types of experiments. My microscope and other tools allow me to do other sorts of experiments. My computer allows me to do yet others. I consider all of these things to be parts of my research lab. Biology is a complicated and wide-ranging subject area that can be approached from many directions.

I expect I'll keep finding things to discuss on a weekly basis for quite some time. I also expect my thoughts will continue to cover a range of topics not always traditionally associated with biology.

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I visited central Alaska around the summer solstice in 2015. I took a lot of photos of the city and in particular of the plants I came across. Though I've tapered off with this topic, I still have a series of posts that I'm still trying to find the motivation for.

Bunchberry (Cornus canadensis, "Dwarf Dogwood") is the smallest species of a widely distributed genus of small-to-medium sized trees. This species grows over a broad swath of the northern edge of North America (Canada, Alaska, Minnesota, etc.).

Where I live in Minnesota is at the southern edge of the plant's range, where it only grows marginally. I find the occasional specimen growing in heavily shaded woodland sites in some local parks.

In central Alaska, the plant grows wildly. Large and dense patches were found growing along some exposed road-sides near the tree-line at high elevation. It was also growing widely in the shaded woods near where I was staying, just as more scattered populations than the ones at higher elevations.

Later in the season, the pollinated flower clusters develop into tightly-packed bunches (hence the name "Bunch"berry) of bright-red berries. The berries are technically edible, but they have a large seed and are pretty much tasteless. In general, I'd say they're not worth the effort to gather. However, I'd probably taste a sample of the berries if I came across a patch in the hopes of finding one that did taste good, because who knows, I might get lucky.

Botanizing in Alaska: Northern Monkshood

This flower was found growing on the same exposed rocky slope as a few of the plants I previously posted about (http://the-biologist-is-in.blogspot.com/search/label/rocky slope). It is the very pretty, but also deadly, Aconitum delphiniifolium (Northern Monkshood). The plant survives for several years, spreading slowly by producing daughter tubers.

The toxins produced by plants in this genus (aconitine, mesaconitine, hypaconitine, etc.) bind to the voltage-sensitive sodium channels of nerve cell axons. Upon binding, the toxin forces the channels open and over-stimulate nerve signals until the cells can't respond any further. The cells then fail to send the signals necessary to maintain breathing or the hear-beat and death soon follows without aggressive treatment. At this stage, you will need cardiopulmonary bypass in order to have a good chance of surviving. All the while, you will be hallucinating madly and so will be unable to seek or assist in treatment.

Seriously, don't eat this plant. That said, it is quite pretty.


References:

• www.alaskawildflowers.us/Kingdom/Plantae/Magnoliophyta/Magnoliopsida/Ranunculaceae/Aconitum_delphiniifolium/index.html
• www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500017
• www.ncbi.nlm.nih.gov/pubmed/19514874

Botanizing in Alaska: Claytoniella bostockii

I've previously posted about a couple of plants from a shattered-rock slope we encountered outside of Fairbanks (the-biologist-is-in.blogspot.com/2015/07/botanizing-in-alaska-dwarf-birch.html; the-biologist-is-in.blogspot.com/2015/07/botanizing-in-alaska-mountain-avens.html). Though I had taken a break from posts about the biology I encountered on my Alaska trip, there remain still several to go from this site alone.

This particular plant was Marie's favorite. I was eventually able to identify it as Claytoniella bostockii, a plant in the Purslane family (Portulacea). It is a native plant to the area, but doesn't seem to have any common names in English.

It appears to grow perennially, regenerating from roots every year. There were many small plants in addition to ones as large as seen in the second photo, which presumably took several years to grow. I'm certain there are biologically interesting things about this plant, but I didn't spend any real time examining the actual plants so I can't add to the paltry amount of information available online. Maybe on the next trip, I'll take better notes.


References:

• the-biologist-is-in.blogspot.com/2015/07/botanizing-in-alaska-dwarf-birch.html
• the-biologist-is-in.blogspot.com/2015/07/botanizing-in-alaska-mountain-avens.html
• www.arcticatlas.org/photos/pltspecies/spp_details.php?queryID=mobo

Botanizing in Alaska: Fireweed

Fireweed (Chamerion angustifolium) is a stereotypically Alaskan wildflower, though it does grow widely in the northern regions of North America, Europe, and Asia. It grows luxuriantly in newly-opened areas the year after a wildflower, hence its name.

The plant usually flowers in dark pink. I found the light pink form at an incidence of roughly 1:100,000 plants during my Fairbanks trip. (Very rough estimation from observed density in an open field where this photo was taken.) I saw one small patch of just the lighter shade, but it was along the highway where I was not able to stop and take photos.

I had hoped to gather seeds for my garden, but none were to be found during my trip. The seeds mature well after all the flowers have withered away, so I would have to plan a trip later in the season if I want to find any. Since the light-colored form of the plant would look no different from all the others, I'd have only the slightest chance of getting seeds for this novel form.

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My research indicates Fireweed can also be found in my home state of Minnesota. I'd never noticed it before, but since I've seen it up close recently...  I've now noticed a few isolated patches of what looks like a smaller version of the Fireweed I saw in Fairbanks. Unfortunately, the patches were along highway margins, so I didn't have the opportunity to examine the plants in detail.


References:

• en.wikipedia.org/wiki/Chamerion_angustifolium
• www.fs.fed.us/wildflowers/plant-of-the-week/chamerion_angustifolium.shtml
• users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/Hardy_Weinberg.html

Botanizing in Alaska: Peonies

Herbaceous Peonies

Peonies are a well-known early spring flower here in Minnesota. They jump out of the ground early and set about producing a wonderful, but short, bloom display. If you're lucky, the foliage will stick around for the rest of the year, but no later blooms will ever form. They don't grow in the South because the plants need a deep winter cold to trigger development of flower buds.

Herbaceous Peony

What isn't so well-known around here is that they represent the first agricultural export industry in Alaska. Peonies can survive dramatic cold. They shrug off the -60F winters of central Alaska as if it was a balmy -20F. The cold and long winters do delay when the plants start blooming, so they're blooming in mid-to-late summer - a time when no other grower can produce peony blooms. Pair the timing advantage with the huge flowers produced by the plants when growing in near 24-hour sunlight and you have the start of a great business model. If you want peony flowers in July through September, you will have to get them from Alaska... for upwards of $4 a stem because of the dramatic demand for them.

While we were in town, we decided to visit the small Georgeson Botanical Garden at the University of Alaska, Fairbanks. It was here where the initial research about how to grow peonies in Alaska took place, thus it was here where the entire Alaskan peony industry... took root.  (Sorry, I couldn't help it.)

The common peonies are called herbaceous peonies because they don't grow woody stems and die down to the ground each winter. There are so-called "tree peonies" that grow into long-lived medium-sized shrubs, but they're not so cold-hardy and can be expensive to get.

Intersectional Peony #1

Intersectional Peony #2

There are also the intersectional peonies, derived from hybrids of  the herbaceous and tree peonies. They have a herbaceous style of growth, but produce stronger stems that are better able to hold the heavy flowers upright. They also introduce some yellow and orange shades into the more typical whites and pinks of herbaceous peonies. Unfortunately, the intersectional peonies are strongly sterile, so it is difficult to do breeding work with them. New intersectional hybrids have to be created, rather than simply breeding among the ones we already have.

I wonder if the sterility could be resolved by a genome duplication step (the-biologist-is-in.blogspot.com/2015/01/hybrid-sterility-and-speciation.html). The resulting plants would still remain reproductively isolated from the more common herbaceous peonies, but then active breeding work could be performed by more typical means. With the ability to recombine traits in these plants, I could imagine the yellow and pink pigments being blended into a lovely bright orange someday.


References

• www.adn.com/article/20140427/peonies-blooming-business-alaska-growers
• www.alaskapeonies.org/
• www.facebook.com/pages/Alaska-Peony-Growers-Association/237746179638398
• georgesonbg.org
• tree peonies: www.uvm.edu/~pass/perry/trpeony.html
• intersectional peonies:
• www.ilovepeonies.com/About_ITOHS.html
• www.solarisfarms.com/Peony%20Intersectional%20Main%20Page.html

Botanizing in Alaska: Crowberry

This little plant was growing all over the place along the tree-line at one mountain we drove up. It grows as a low-creeper, through and over the mosses and other low-growing plants in its habitat.

The few green berries I saw will eventually ripen to a shiny black which lends them their name of Crowberry (Empetrum nigrum). Though some books I've read indicate the berry is barely edible, much of the information available online suggests the berries are a prime edible. I suspect personal differences in taste may explain the differences in reporting about the berry, though I wonder if some cultural baggage (the-biologist-is-in.blogspot.com/2014/12/black-nightshade.html) may also be involved. I'll have to arrange for one of my next trips to central Alaska to be during berry season so I can find out (at least for my tastes).


References:

• www.uaf.edu/files/ces/publications-db/catalog/hec/FNH-00117.pdf
• en.wikipedia.org/wiki/Empetrum_nigrum

Botanizing in Alaska: Yellow Paintbrush

I found this plant growing up at the top of a mountain, where we were starting a four-wheeler trip from. I recognized it as a paintbrush flower (genus Castilleja), though I had never before seen one this pale. The genus contains some 200 species that are often difficult to distinguish. The populations of various species grade into each other, with intermediate forms confusing identification even further.

There are three Castilleja species noted as living in Alaska: "Yellow Paintbrush" (C. unalaschensis), "Mountain Paintbrush" (C. parviflora), and "Scarlet Paintbrush" (C. miniata). C. parviflora and C. miniata are generally found in shades of red or pink, so I'm pretty sure I found an example of C. unalaschensis. The "Yellow Paintbrush" grows through much of southern Alaska, where it is typically seen in shades of yellow to pale orange. It seems to be closer to white around Fairbanks, however.

Paintbrush flowers, in all their shades, are lovely wildflowers. The most interesting thing about them to me, however, is that they're parasites. They have specialized roots called haustoria that grow into the roots of other plants to steal moisture and nutrients from the victimized plant. They're not a seriously aggressive parasite and could theoretically live on their own, but they definitely get a boost by feeding off a neighbor (who does suffer from the process). This Paintbrush could have been feeding on all the other plants visible in the photo, as they don't specialize on one type of plant.

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I reached out to a Castilleja specialist hoping to get some better idea of the identification for the plant I found. I was surprised at how quickly he responded with very useful information.

Hi Darren,

You mentioned in your blog that there are three Castilleja species in AK, but that is not correct. Besides the three you listed, there are C. pallida, C. elegans. C. raupii, C. chrymactis, and C. hyperborea. Your plant is either C. unalaschensis or C. pallida (also known as C. caudata in some Alaska references). It matches C. unalaschensis (which is usually yellowish) in the somewhat compact inflorescence, but the color is closer to that of C. pallida. It's definitely one of those two, but I can't offer a definitive without more photos, particularly close up ones. If I had to choose, I'd call it an unusually pale form of C. unalaschensis.

Best wishes,

Mark

His response highlights the need to take excellent photos for identification purposes. It helps to know what the key parts of the plant to photograph are in advance as well. I didn't even recognize this plant as a Paintbrush until I was reviewing my photos, well after the trip was over. Next time I promise to get better and more-informed photographs.

Thanks again, Mark!

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References

• Alaska flowers: www.alaska.org/expert-advice/plants-flowers
• Yellow Paintbrush (Castilleja unalaschensis):
• www.solsticelight.com/aks/gallery/matvalley/flowers/yellowpaintbrush.html
• www.flickr.com/photos/mark_egger_castilleja/sets/72157625626420175/
• Mountain Paintbrush (Castilleja parviflora)
• www.alaska.org/advice/small-flowered-paintbrush
• en.wikipedia.org/wiki/Castilleja_parviflora
• Scarlet Paintbrush (Castilleja miniata)
• www.alaska.org/advice/scarlet-paintbrush
• en.wikipedia.org/wiki/Castilleja_miniata
• Other Paintbrush species:
• en.wikipedia.org/wiki/Castilleja
• www.flickr.com/photos/mark_egger_castilleja/collections/72157617709816218/
• Parasitism:
• oleaeuropea.wordpress.com/2011/07/27/indian-paintbrush-a-pretty-parasite/
• kdhnews.com/opinion/columns/outside_insights/paintbrush-flowers-pretty-parasitic/article_18dfb3aa-cf71-11e4-8188-f3ced65f321a.html

Botanizing in Alaska: Twin-Flower

This plant was found growing on my fiancé's father's property. It goes by the name Twin-Flower (Linnaea borealis) due to the tiny paired flowers it produces. The flowers are short-lived, making it lucky that I was able to find and photograph this specimen. By the end of my week in Alaska, every flower in the patch had fallen.

The plant grows as a woody vine, growing up to a couple meters long. It doesn't climb like most vines, however. The plant spreads out into a wide mat, with each branch growing new roots periodically. It likes to grow under conifers, and is often found overgrown with mosses.


References:

• http://www.arkive.org/twinflower/linnaea-borealis/ 
• http://plants.usda.gov/core/profile?symbol=libo3

Botanizing in Alaska: Dwarf Birch

I found this tree trunk on a rocky outcrop at the top of a mountain just outside Fairbanks, Alaska. The wood was spread over a foot or so, though I didn't have a measuring-tape handy to get a precise measure. The cold and exposed environment suggests that the tree would have grown very slowly and may be anywhere from decades to hundreds of years old.

In this environment, strong winter winds quickly abrade away overly-exposed living material. Dead material doesn't last very long either. Yet this tree remains alive, with vital growth attached to the dead wood at the lower-right and upper-left.

It was only by comparing the above tree to something more youthful (at right) that I was able to identify it as the Dwarf Birch (Betula nana). Forests of this tree can be ancient, but only inches tall.


References:

• https://en.wikipedia.org/wiki/Betula_nana
• http://www.fs.fed.us/database/feis/plants/shrub/betnan/all.html
• http://plants.usda.gov/core/profile?symbol=BENA

Botanizing in Alaska: Mountain Avens

The Mountain Avens (Dryas octopetala) is a circum-arctic subshrub, growing up to a meter across while reaching only a few centimeters tall. The flowers typically have eight petals (hence the name octopetala) and track the arctic sun as it rolls around the summer sky. This heliotropism is thought to help the flower warm up so it can mature its seeds more quickly. There are several subspecies, including the Alaskan form (D. octopetala ssp. alaskensis), but little information is available about the differences between the forms.

Since I found them after the flowers were long gone, identification was a bit trickier. The seed-heads reminded me of those from the Pasqueflower (Pulsatilla), so I started my searches there. The leaves are distinctly different, however, so I meandered into looking at images of arctic wildflowers from Alaska until I found an image that had the right leaves. I was lucky in that the site included an ID of the plant, which I rapidly confirmed elsewhere.

Supposedly the plant takes well to garden culture, though its short-stature would make it sensitive to being overgrown by aggressive weeds when in a warmer climate. I did collect a few seeds, so I hope to see how it does here.


References:

• https://en.wikipedia.org/wiki/Dryas_octopetala
• http://www.fs.fed.us/wildflowers/plant-of-the-week/dryas_octopetala.shtml
• http://www.flora.dempstercountry.org/0.Site.Folder/Species.Program/Species2.php?species_id=Dryas.octo

Botanizing in Alaska: Wild Iris

I just returned from a week-long trip to Fairbanks in central Alaska. I quickly noted the abundant wild irises (Iris setosa interior) in bloom around the city. The species is endemic through much of Alaska, with a few regional subspecies/varieties. It goes by a few different common names. "Beachhead Iris" seems to be the most common, though I prefer "Alaska Iris" for the plants I encountered because it more clearly refers to the specific Alaskan sub-species.

While I was there, the local paper (Fairbanks Daily News-Miner) published an article about Jack Finch, a metalworking instructor at the local university, who has a long-running hobby of breeding I. setosa.

www.newsminer.com/features/our_town/an-eye-for-irises-grower-pulls-a-rainbow-of-varieties/article_db950be2-1d65-11e5-8207-4ff1af2d6​4db​.html

Though we tend to refer to all the colorful floral structures of a typical garden iris as "petals", the structures are botanically divided into the true petals (upright standards) and petaloid sepals (descending falls). In I. setosa, the botanical petals are reduced so severely that the flower appears to have only three "petals". Jack Finch occasionally sells plants in Fairbanks, which probably helps explain the diversity of colored forms I found in gardens during my week.

NewsMiner photo.

In addition to numerous shades, Jack Finch also isolated a recessive mutation which converts the tiny petals of the wild flower into full-sized sepals (thus producing an attractive and larger flower). I never did find an example of this flower, but the newspaper published a photo which nicely illustrates the variation.

During my trip I was able to collect seeds from several plants with different colored flowers. As the plants were in full bloom, the only seeds to be found were those left-over from the previous season or two. Hopefully they remain viable so that when I plant them this fall (for cold-stratification) they can start growing in spring.

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The Iris genus is subdivided into several sub-genera, which are then in turn subdivided into several series of species. For the wild Iris setosa I was so admiring, the full nomenclature is something like: [Genus = Iris] [Subgenus = Limniris] [Series = Tripetalae] [Species = setosa] [Subspecies = interior].

Species definitions in plants are often less strict than they seem to be for animals. Some research from a few years ago sought to identify how I. setosa was related to other North American wild irises. They found I. setosa was most likely one of the parents (with I. virginica) of I. versicolor. I. setosa and I. virginica are both diploid with 38 (19/19) and 70 (35/35) chromosomes, respectively. The hybrid between the two species is infertile due to mis-paired chromosome sets (19/35). But like in other cases (http://the-biologist-is-in.blogspot.com/2015/01/hybrid-sterility-and-speciation.html), that infertility can be resolved by a whole genome duplication like that which appears to have happened in the ancestors of modern I. versicolor.

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References:

• https://en.wikipedia.org/wiki/List_of_Iris_species
• https://en.wikipedia.org/wiki/Iris_setosa
• http://www.fs.fed.us/wildflowers/beauty/iris/flowers.shtml 
• http://www.ncbi.nlm.nih.gov/pubmed/17591610