...said the visitor, “Broom isn't a climber, surely? It grows on heaths, doesn't it?”
Yes it does - but in certain circumstances, and with certain species, it can also grow on walls! The photos show Pineapple Broom, proper name Cytisus battandieri (a name which always makes me think of Flamenco for some reason... or cake), which makes a lovely wall-trained shrub but needs to be in a sheltered area, as it is not fully hardy.
Isn't it lovely? I could see her confusion, though: a lot of people aren't sure about the difference between Broom and Gorse anyway, and she asked me to explain it to her.
Never one to miss an opportunity to discuss botany, I explained that when discussing Broom, we always have to start with the question:
Broom, Whin or Gorse?
All three are more-or-less evergreen shrubs, bearing yellow, pea-like flowers which explode when insects alight on them, thus pinging the pollen all over the hapless insect. They all grow in the wild (except for my tender Pineapple Broom) on disturbed soil, often at roadsides, on scrubby, dry heaths and on rough grasslands. So how do we tell the difference?
Gorse (Ulex) have no normal flat leaves at all, other than on very young plants: mature plants are covered in branching green spines, which provide photosynthesis and protection all in one.
Whin (Genista) have green leaves which are oval or oblong, along with a few simple (unbranched) spines. The leaves are sessile, which means stalk-less: they are attached directly to the stems, one by one.
Broom (Cytisus) is completely free of spines and rather erect, with long green five-angled stems, carrying stalked green tri-foliate leaves - that means each leaf has usually three leaflets, rather like Clover - on younger stems. Older stems tend to be bare of leaves.
Like everything to do with botany and gardening, the confusion arises because we all use the common names, and we often use them wrongly. For example, the names gorse, furze and whin are all used interchangeably to mean gorse - which is Ulex. But officially, whin is Genista: it's a different genus, it has leaves, and few spines. And in Scotland, “broom” is Ulex (gorse - or whin, or furze) whereas actually Broom is Cytisus, which has very different leaves and no spines at all!
Still confused? It gets easier: Genista (Whin) likes limestone grasslands, which are alkaline in nature: whereas Gorse (Ulex) prefers acidic soil, such as heathlands. So, if you know what sort of underlying soil you have, you can make a guess as to whether you are looking at Gorse or Whin. And if has tri-foliate leaves, it's neither!
They all have very similar flowers, but flower at slightly different times. Both Broom (Cytisus) and Whin (Genista) flower in the early summer, from May to June. The two less common types of Gorse - Dwarf Gorse, U. minor and Western Gorse, U. gallii - flower later in the summer, from July to September. But common Gorse, U europaeus, flowers pretty much all year round, if it's fairly mild. Which lead to a popular folk saying: ‘When gorse is out of blossom, kissing’s out of fashion’. It’s a knowing wink to the fact that, in milder areas, gorse can flower all year round - so kissing never goes out of fashion.
And finally, a quick word about Broom in popular culture: back in the 1800s, the Victorians were accustomed to using flowers to send secret, coded messages during a time when young ladies were not allowed to fraternise with young men (ah, how times have changed!), and liaisons had to be arranged discretely and modestly. Sending a Broom flower represented Humility and Neatness: presumably at that time, those were desirable qualities. Not so much, these days!