You have just read the heading and I can hear your mind working overtime. What the hell is a Spiny Emex? You're conjuring up all sorts of visions as to what this animal looks like and is it as dangerous as it sounds. An animal it isn't, a danger it is. Probably not so much a danger as a downright nuisance, especially if you are cycling on a country road. You may not even see it until it is too late and either you hear the air hissing out of your front tyre or you suddenly feel the bumpity bump of a flat tyre and even worse, both tyres. I don't know whether even kevlar lined or similar puncture resistant tyres would be much help in preventing these little fellows from penetrating a tyre.
The Spiny Emex or as it is commonly known, the 'Three Cornered Jack' is a weed, the fruit of which can be described as having 3 spines and being 7-11mm long.
It doesn't seem to matter which way they land on the roadway one side is always pointing upwards just waiting to snare an unsuspecting cyclist's tyre. There is little a cyclist can do to prevent an incident involving a 'Three Cornered Jack', it just goes with the territory. Unless they are still attached to a branch of the weed, it is highly unlikely you would see them. Just ensure you carry a good puncture kit. If nothing else, this information may help identify the cause of the puncture, particularly if you haven't seen any glass on the road and you happen to get multiple punctures in a short period of time.
As can be seen by the map, the weed is more prevalent in some areas than others.
On the lighter side......Mark Twain - Wisdom on Cycling, "Learn to ride a bicycle. You won't regret it if you live"
Enjoy your cycling, relax and make it safe.