The stem. It's taken root on bags, tablecloths and gumboots, iPhone cases, radios, cars and London buses. You see it in the Tate, John Lewis and Uniqlo; it's a collector's item, seasonally morphing into new colours and guises, and you'll find it in New Zealand in boutiques, homeware and gift stores.
Yet the woman behind this ubiquitous sprig and leaf motif is a bit of a shrinking violet. "People know my prints but they don't know me, which is a good thing," Orla Kiely says, when I meet her at her studio in south London. "I never have to worry about being recognised."
I agree that you wouldn't immediately place Kiely (pronounced Kylie) as a fashion mogul. There she was at our meeting: no blow dry, no facelift, no Prada suit or killer heels, just a pair of burgundy Doc Martens and a sleeveless black dress with applique flowers.
The only clue is her beige, white and black printed turtle neck, part of a collaboration collection she has done recently with Uniqlo. "I usually wear some kind of print," she says. "It adds personality but not in a cheesy way. Depending on the print it can make any outfit that little bit more glam."
Print - simple, strong and graphic, nothing bonkers - is Kiely's big thing. She grew up in rainy Dublin, knitting or crocheting while watching vintage films starring Catherine Deneuve and Mia Farrow. "My inspiration has always been Mid-Century. I love the way the women dress in all the kitchen sink dramas, and films such as Rosemary's Baby and Barefoot in the Park."
The clothes she designs - and wears every day - reflect this: printed pencil skirts, collared dresses with belts in yellows and blacks, velvet patterned handbags with Bakelite closures. "You feel so self-conscious if you wear something that's not you, it's the worst feeling," she says.
"The prints I wear tend to be quite tonal - they can look like a solid until you see that they're a pattern close up. If I've got an important appointment I put on one of our dresses with a dash of red lipstick and off I go."
Alexa Chung and Kirsten Dunst are fans of Kiely's 60s-inspired pieces, and so keen is the Duchess of Cambridge on one of her Orla Kiely outfits (she owns several), a brown dove-print wool dress, that she was pictured wearing it recently for a second time since she bought it in 2012. "It's wonderful that she wears my dresses; she looks absolutely great in them," Kiely says.
For more than a decade, Kiely has been a household name - a way of life, even - yet she still glances around her office almost incredulously at the box files, cuttings boards, and Orla Kiely products spilling from the shelves. "It started as a tiny sideline," she says. "I didn't have any contacts or factories or printers."
Her first job was as a print designer for Esprit and then she embarked on an MA at the Royal College of Art. It was her husband, Dermott Rowan, who worked in finance at the time, who persuaded her to start her own label. "He believed in me much more than I did," she says. "I'm so supercritical - but he really did think it could happen."
Kiely still struggles in this respect. While she pauses to send a lengthy text message to the youngest of her two sons, Hamish, 16 (there's some issue about a concert he's off to), I take in the motivational phrases papering the walls of her enormous office: "Be confident in yourself";
"Have your own opinion"; "Always finish what you started" - mantras she hopes her customers share. "I truly believe that confidence, style and beauty come from within," she says.
Rowan and Kiely started their business quietly - I can't imagine Kiely doing it any other way - when she graduated from the Royal College, buoyed by Harrods buying her degree show. "I'd made these rather cute boiled wool beanies and they went down well," she says. "So we found a factory to make a small run of them."
Kiely was then offered a job with Club Monaco in Canada and they moved across the Atlantic, where they continued to nurture their fledgling business, Rowan quitting his job to focus on it full-time.
When they returned to London a year later, Kiely several months pregnant with their eldest son, Robert (now 19), they began producing printed cotton canvas bags as well as hats. "My father had come to see our tiny stand at London Fashion Week and his observation was that everyone was carrying a bag but they weren't all wearing hats," she says.
The inaugural Orla Kiely prints were an egg shape and a flower. "We found a factory that was prepared to do a small run of the sweetest backpacks and body cross bags," she says. It was as if they'd struck gold. The bags were a sell out.
Next summer the stem "just sort of happened". "We put it on cotton canvas bags and everybody loved it," she says. Then she came up with the idea of making sturdier, laminated bags - the first of their kind - also with a stem print.
"Everybody loved them so I started taking the stem more seriously," she says. "We were just going from season to season but now we decided to turn the stem into a vehicle for the brand that we could change. Reinventing it has become a quarterly challenge but it always seems to work out - just when I think there is nothing more we can do."
Rowan still handles the financial side of the company - he's currently out in Japan expanding the empire - leaving Kiely to focus on print. While she admits the stem has been good to her, it's only a small part of the brand - each season she aims to design at least seven new prints.
"I never get bored of coming up with new prints. The simpler they are, the more difficult they are to design," she says. There have been boats and birds and pears and acorns, in an array of colours. "I'm drawn to opposites - blue and red, pink and green, yellow and black."
Not that you'll ever catch Kiely wearing more than one statement print at a time. "I'm always interested to see how people wear my clothes. If I'm wearing something bold, the rest of my outfit is understated."
How does she ensure her prints are flattering? "It's all about the silhouette and this depends on choosing the right fabric," she says. One of her favourite pieces is a shirt dress made of structured cotton. "I always worry that I'm going to look huge under it but the skirt pops out in such a flattering way. I can wear it to a fancy dinner or to work with my flats."
Just occasionally, she does venture away from her own brand, usually into Prada, Marni or Dries Van Noten. But by and large she sticks to Orla Kiely, not just in terms of what she wears, but how she lives. The house she shares with Rowan, the boys and her labradoodle Olive, within walking distance of her office, is an Orla Kiely showcase, with stem-print cushions and tables and her giant rhododendron wallpaper.
Does she ever worry about print going out of fashion? She looks at me in horror. "No, do you?" I glance around her office, at the stem-printed scent bottles, candles, notebooks and lampshades and shake my head.
ORLA KIELY'S STYLE
Your clothes are from?
Liberty, Harvey Nichols and Dover Street Market.
How do you shop?
Instinctively and decisively. If I like it, I'll buy it.
Red carpet look?
Valentino or vintage couture, not that I ever walk on the red carpet.
Most expensive luxury?
I'm too sensible but in an ideal world, beautiful Prada dresses.
A dress with a blouse underneath it or a shirt dress.
Flats or heels?
Flats 90 per cent of the time.
Mia Farrow or Audrey Hepburn.
Less is more.
Your secret weapon?
Best style advice?
The woman should wear the dress, not the other way round.