“Yellowtop” or “Fireweed”?
Which yellow daisy is which?
Senecio brigalowensis, BRIGALOW YELLOWTOP (Native, annual)
Senecio pinnatifolius var. pinnatifolius PERENNIAL YELLOWTOP (Native, biennial or perennial)
Senecio madagascariensis*, Madagascar fireweed (Non-native, annual or biennial, a serious weed)
The countryside around Toowoomba is ablaze with yellow daisies at the moment. There are three species involved, but from a distance, the plants seem almost identical.
To some people, they are all “fireweeds” and are treated as equally undesirable.
Two of the three species are native, however, and are important hosts for some beautiful and increasingly rare native insects. (See http://toowoombaplants2008.blogspot.com/2017/06/mountain-katydid.html or search for Mountain Katydid, Acripeza reticulata).
So which yellow daisy is which?
It is quite easy to distinguish Madagascar fireweed from the other two species by the shape of its leaves. All Senecios have leaves of a rather variable size and shape, but if you are trying to tell one yellowtop/fireweed from the others, look for the leaves around the middle of a fully-grown plant. They will still be variable, but you can get a good idea of the most common leaf shape.
The leaves of Madagascar fireweed (Senecio madagascariensis*), are spear-head shaped, with teeth, as below: 
The leaves of both the native species have long thin lobes, which gives them a “whiskery” look.
The leaves and leaf-lobes of Perennial yellowtop (Senecio pinnatifolius var. pinnatifolius) tend to be narrower than those of Brigalow yellowtop (Senecio brigalowensis), but there is some overlap so this is not a reliable guide. If the “whiskers” of the leaves have any very tiny teeth on the edges, you have Brigalow yellowtop, but many brigalow yellowtops have no teeth - just the long, thin, thready-looking lobes as above.
The most reliable way of distinguishing between the two natives is to count the bracts (not the petals). The bracts are the tiny green strips which make up the green cup in which the daisy flowerhead sits. You may need a good pair of reading glasses to count them, and at first though this seems like a hopeless task.
However brigalow yellowtop (Senecio brigalowensis) has more than 18 bracts and in practice there are usually about 22 of them. Our local (Darling Downs) perennial yellowtops (Senecio pinnatifolius var. pinnatifolius) have only about 13. Really, by the time you are half-way round you are going to know whether the full count is going to be more like 13 or 22, so it’s not that hard after all. Can you see, by the photo above, that you are looking at perennial yellowtop? Enlarge the photo and you can see only 6 or so bracts on this side. There is not going to be room for a total of 22 altogether, so you hardly need to count them all the way round! The bracts of the perennial yellowtop also tend to be purple-tipped, but this is not always a reliable indicator.
Perennial yellowtops flower later than brigalow yellowtops, and don't tend to produce such a crowd of plants. Their petals are also somewhat longer and slimmer. Once you know both plants you will find you can distinguish them at a glance.
MADAGASCAR FIREWEED Senecio madagascariensis*
Poisonous to horses, cattle, pigs and poultry.
If you have this one, you should get rid of it as soon as you can. It can have SIX GENERATIONS of seed per season. (Native yellowtops breed at a more civilised rate, only producing one generation of seed per season.) You can see why a few Madagascar fireweed plants might turn into a rather big problem rather quickly.
To make it worse, if you pull out plants with flowers but no seed on them, any flowers can mature and produce viable seed while they are drying out in your garbage bin. The seeds have fluffy tops designed to blow in the wind, so those plants that you thought were safely disposed of will spill seed even as your friendly helpful garbo is tipping your rubbish into the truck. The moral of the story is that all Madagascar fireweed flowers, as well as seeds, should be carefully placed into a sealed plastic bag for disposal.
BRIGALOW FIREWEED Senecio brigalowensis
Poisonous to horses, cattle, pigs and poultry.
Every few years in spring we have a big flush of these flowers, and this year is a biggie. Our paddocks and some road verges are sheets of yellow. They do like disturbed land. If you want to see a really good display, drive around the northern edge of Toowoomba on the new bypass road. You will notice how the road verges are a mass of colour, but very few plants have spread to the other side of the fence. The same can happen between one paddock and the next, which tells you some things about those paddocks’ different histories or use patterns. Heavily grazed paddocks are more prone to a big flush of yellowtops.
The curious thing is that it is only in some years that we have these big flushes, and it has only been happening here since 2007. Nobody is sure why, but it probably has something to do with our changing climate.
Unless you (or you neighbours) have horses or cattle, these lovely wildflowers can be left alone for you to enjoy, and for small native creatures to feed upon. They are part of our natural Australian environment.
Don’t feed them to the chooks, though.
PERENNIAL FIREWEED (Senecio pinnatifolius var. pinnatifolius Syn Senecio lautus ssp. dissectifolius)
Not regarded as dangerous to livestock.
This plant flowers a little later in the season, and never reaches pest proportions. You will notice it scattered about in paddocks which are grazed by cattle, with no resulting problems. In a well-managed (not overgrazed) paddock, such as the one in the photo below, they are not a problem. Perhaps they taste nasty, so cattle avoid them unless they are in a situation such as a stockyard or stock route, where heavy grazing leaves them with little choice of fodder.
They are a local wildflower to celebrate. What a pity that the issue of whether or not to let them grow is so confused by their weedy relatives.
