杏吧原创

THIS is a cautionary tale. Several years ago, I had a most uncomfortable
experience. Our local supermarket was selling mangoes at bargain-basement
prices, so every day for weeks I ate two or three of them. One day, after
finishing off several of the succulent fruits, my nose began to itch, my lips to
swell. Less than an hour later, my lips were huge and my nose felt as though it
belonged to Mr Potato Head. At that time I was, as far as I knew, allergic only
to poison oak and poison ivy. So what had happened? As it turns out, mangoes and
poison ivy are members of the same family鈥攂oth cousins of the cashew.

The American authority on pollen, Walter Lewis, once saw one of his students
go into anaphylactic shock after drinking chamomile tea. She flushed red,
coughed, choked and started to suffocate as her airways began to close. Luckily,
she recovered, and when skin-tested, she showed a strong positive reaction to
ragweed, a relation of chamomile.

In clinical tests on people allergic to ragweed, about 30 per cent test
positive for allergy to goldenrod if there is any growing near where they live.
Why? Once again it鈥檚 a case of kissing cousins: ragweed and goldenrod both
belong to the sunflower family.

Perhaps the worst example of this cross-reactivity is peanuts, infamous for
the severe鈥攕ometimes fatal鈥攔eactions they provoke in people allergic
to them. They鈥檙e a legume, and all legumes are related. Allergies to peanuts are
on the rise, as is sensitivity to products derived from soybeans, another
legume. Cases of cross-reactivity between allergies to food and pollen, and
those to pollen and legumes, are also increasing. This is particularly worrying
because someone who鈥檚 allergic to peanuts should be very careful about what they
plant in their garden.

Legume pollen is one hazard. Most legumes are pollinated by insects, but many
are both wind and insect-pollinated, and some produce male flowers that release
pollen into the air. And as legume pollen is sticky and relatively heavy, it
doesn鈥檛 usually travel far. Up close, though, it could be dangerous.

Then, there is the sheer number of the things: more than 12,000 species, with
many used in landscaping. Most are spring and summer bloomers. Southern species
include acacia, mesquite, palo verde, carob and mimosa, while catalpa, locust,
laburnum and gleditsia are grown in colder climates. Legume trees can all cause
allergies but acacia, mimosa, mesquite and catalpa are the worst.

How did we get into this mess? One of the most likely causes is over-planting
the same landscape species. In the US, for instance, highway departments line
freeways with acacia. Landscapers often use the same few dozen species in their
schemes. Clearly, we need reminding that when it comes to combating allergy,
biodiversity is all.

So pester the people responsible for your urban landscape to inject some
variety into it. But don鈥檛 forget: the best place to start is nearly always your
own backyard.