HytestA said:

I have just moved into a new house with my wife and daughters, we have a
nice garden but its been a bit neglected over the years by the previous
owner and whilst going over it my wife noticed we have an abundance of a
strange plant that we dont recognise. It looks a bit mushroom like but
its 'cap' is hard, and when mowing the lawn my wife said that it looked
like it emited smoke or spores.

Yes, it is emitting spores. Equisetum (horsetail, scouring rush) are plants
that reproduce by spores rather than seeds. They are often referred to as
'living fossils' as they were the dominant type of land-plant hundreds of
millions of years ago.

http://en.wikipedia.org/wiki/Equisetum

One of our main worries is for our young daughter who will be starting
to use the garden in the summer and we want to know what this plant is,
if its dangerous and how to get rid of it. Any help identifying it will
be most appreciated.

It's not particularly dangerous for humans, though it can be toxic to
sheep and horses as a contaminant in hay.

The 'getting rid of it' is going to be very hard. The underground part of
the plant is wiry and tenacious and herbicides like Roundup not particularly
effective (it helps to bruise the horsetails before spraying).

http://www.agf.gov.bc.ca/cropprot/hrsetail.htm

http://www.gardenguides.com/854-horsetail-weed.html

--
Pat in Plymouth MI

"Vegetables are like bombs packed tight with all kinds of important
nutrients..." --Largo Potter, Valkyria Chronicles

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