Catherine StewartHow to identify a mystery plant

I’m asked all the time to help people identify plants. Even though many of them grow in places way outside my climate zone, I’ve become a pretty good botanical and horticultural sleuth. Recently Keren in Bermuda sent me some photos of a shrub she was trying to name, without success. And I’ve also been thinking about my experiences earlier this year running from one gorgeous wildflower to the next in Yunnan, China, trying to understand what I was seeing. So what sort of characteristics do you need to look at when you’re trying to identify a mystery plant?

Where do you begin?

Keren's mystery plant

Keren’s mystery plant


Close observation of your mystery plant

The first step is observation, and that means learning to look beyond your unidentified plant’s superficial resemblance to a plant you already know. Although seeing those similarities gives you one starting point, don’t let them stop you seeing where they also differ.

I’d liken it to many people’s response when they see me and my older daughter together. “You look so alike!” we’re often told. As she’s much prettier than me and also 28 years younger, I gratefully accept the compliment but then am compelled to ask them to look more closely. Is her face shape like mine? Her brow, her eyes, her nose, her mouth? No, on all counts. Alas, what makes us look alike is pretty much only our colouring as we are both fair-skinned, strawberry blonds (well, I was). The similarity of our colouring has overwhelmed their other observations.

In Keren’s case, it was her plant’s superficial resemblance to a Clerodendrum (especially Clerodendrum mastacanthum) that was confusing and she’d been told by a number of local gardeners that’s what she had growing in her garden. Yes, the flowers did look similar…and yet…and yet…to me, something about that ID was just not quite right.

So make a note of what others have guessed but, for the moment, put aside those identifications and look more closely. You may soon find yourself confronted with a characteristic that’s totally incompatible with the original guess!

Habit of Keren's shrub growing in her Bermuda garden

Habit of Keren’s shrub growing in her Bermuda garden


How to observe a plant:

Although there are dozens of very specific botanical words to describe plants, I’m assuming that most people will have no idea what words like stipule, glabrous, terete and the wonderful infundibular mean. There are still lots of ways to describe your plant in ordinary words that a horticulturist or botanist will understand too.

Type of plant – is it a tree with a single trunk, a multi-stemmed shrub with firm, twiggy growth, or a perennial plant with soft, pliable stems? Of course Nature doesn’t always like to sit in these neat little boxes of our making, but it’s a starting point.

Deciduous or evergreen? Deciduous can mean either that all or most of the leaves drop off at certain times of year or that it dies back down below ground. Or is it an evergreen with permanent leaves?

Age – if it’s in your garden, have you any idea how old it is?

Size – how high and how wide is it?

Habit – this covers overall shape and appearance characteristics like whether it’s a vase-shaped, conical, umbrella-shaped, rounded, spreading, open and twiggy, star-shaped or grass-like.

Stems and trunk – smooth or rough, round or squarish in cross-section, straight or zig-zag? Colour?

Leaf arrangement on the mystery shrub in Keren's Bermuda garden

Leaf arrangement on the mystery shrub in Keren’s Bermuda garden


Leaf arrangement – do the leaves come out from the stem opposite each other, in rings around the stem, or alternating along the stem? Are there any other leafy-looking bits that are different shapes?

Leaf size and shape – are the leaves big (larger than your hand), medium-sized (bigger than a matchbox), small (bigger than a small coin) or tiny (you can hardly see them). Are they long and skinny, short and rounded, curved, twisted, rolled, shaped like a hand or a sword? Is the leaf edge a smooth line or is it bumpy or serrated?

Leaf texture and colour – leathery, thin and soft, papery, smooth, shiny, hairy, downy, scaly, prickly? Are the leaf veins very obvious and in any particular pattern? What colour or colours, and are the new and older leaves different colours?

Leaf aroma – can you smell anything when you crush the leaf? Nice or nasty? Like a fragrance you recognise?

Flowers on the mystery shrub in Keren's Bermuda garden

Flowers on the mystery shrub in Keren’s Bermuda garden


Flowers – size, colour, time of year. Do they have petals or are they tufted like a brush? If there are petals, how many (if you can count them!) and are they all the same shape or are some different to others (perhaps in pairs). Are the flowers single flowers or grouped together – in heads, or spikes, or drooping like a bunch of grapes? Are the flowers scented?

Buds – look for any leaf or flower buds and make a note of their size and colour

Where the plant is growing – country, zone, climate, in a garden or wild, terrain, soil type, sun or shade


Plant Identification on Facebook

Plant Identification on Facebook


Identifying plants using online resources

Have you tried doing a Google image search? It’s surprising how much you can find if you use a ‘long string’ query in the Image Search. That means putting in as many important key words as you can, based on your observations.

And for those who use it, Facebook is also a good place to look for ident help. The Facebook group Plant Identification is used by both home gardeners and experts looking for the names of mystery plants and, in return, offering help in plant identification. It’s a fun (and free) sleuthing exercise that many budding botanists and home horticulturists can’t resist!


Using online herbaria to identify your mystery plant

Many of the world’s botanical gardens have been quietly digitising and online-publishing their libraries of pressed herbarium specimens. These aren’t records that you can browse through, but once you’ve narrowed down your guesses, it’s the place to type in your genus or full botanical name (genus and species) and check whether you’re getting close. What these specimens lack in photographic colour they make up for in accuracy, provenance and detail of all parts of the plant.

Sample of herbarium specimens in Kew's collection

Sample of herbarium specimens in Kew’s collection


Kew Gardens in London has nearly 1 million digitised images of its herbarium specimens, some of them up to 200 years old and many of them the ‘type’ species – that’s the plant that was collected and used to identify the species in the first place. Search Kew Gardens Herbarium

The Missouri Botanic Garden (MOBOT) is another fabulous online digitised resource for searching for plant images through its Tropicos portal. Images include herbarium specimens, slides, drawings and paintings, and photographs.

For Australian plants, PlantNET – NSW Flora online has herbarium specimens, photos and botanical drawings of plants growing wild in NSW, including both indigenous and introduced species.

Australia's Virtual Herbarium sample map

Australia’s Virtual Herbarium sample map


Australia’s Virtual Herbarium is a terrific tool is you know a genus and are trying to find what species grow are likely to grow in different locations. Putting a genus name in the search bar will show you a map of Australia, showing the location of all recorded herbarium specimens in that genus.


Identifying plants using books

As I write and publish online, it probably surprises people how much I still use my garden books. Part of the reason is that a book is edited, referenced and checked and the photos taken by skilled, professional photographers whereas many online resources are of dubious quality and accuracy (except GardenDrum of course) and have poor quality images.

I have a big library of gardening and plant books but the ones I find I pull off the shelf most often are Botanica, an extensive plant reference book published in Australia by Random House in the late 1990s. I have found so many mystery plants simply leafing through its 944 pages. Admittedly it’s a little dated to pick up new cultivars but for identifying species plants it’s very useful. Plus turning those pages and looking at those thousands of photographs every now and then is a very good way to learn your way around the plant world and you will start to pick up important rather than superficial family resemblances.

Garden Plants of the World by Don Ellison

Other helpful references include Don Ellison’s Garden Plants of the World (New Holland 2002), the series of books published by Pan by Roger Phillips and Martyn Rix of perennials and shrubs, as well as Rix’s invaluable Trees in Britain. Australia’s Flemings Nurseries have great online resources but I also like their 2011 printed Fruit and Ornamental Tree Guide.

For tropical plants, 1001 Garden Plants in Singapore (published by NParks 2006) is a great help as is Margaret Barwick’s Tropical & Subtropical Trees (Thames & Hudson 2004).

Tropical and Subtropical Trees by Margaret Barwick


References I use for identifying Australian native plants include: Native Plants by John Wrigley and Murray Fagg; Banksias Waratahs and Grevilleas also by Wrigley and Fagg; Acacias of South-Eastern Australia by Terry Tame; Rainforest Plants by David L Jones; Australian Ferns and Fern Allies by Jones and Clemesha; Climbing Plants in Australia by Jones and Gray; Mangrove to Mountains – a field guide to the Native Plants of South-east Queensland by Leiper, Glazebrook, Cox and Rathie. For my local Sydney plants, nothing beats the bible of Native Plants of the Sydney District by Alan Fairley and Philip Moore.


Identifying plants using people

If you’re taking some pieces of plant to someone hoping for an ID, take a piece of the plant large enough to show as many of these characteristics as possible – stems, leaves, flowers, seedpods/fruit/seedheads and habit. More than just a few squashed leaves in a plastic bag! Here are some useful guides from the Royal Botanic Gardens Sydney on collecting plant specimens for identification. (Collecting Plant Specimens)

If you’re trying to send photographs to someone looking for plant ID, then you need photos of the same types of things  – closeups of leaves, flowers, fruit and seeds are good but you will also need to send photos of the whole plant to show its size and habit and environment. If you’re using a smart phone or especially a tablet/iPad camera, make sure that the important part you’re showing is actually in focus, not the background.

Botanic gardens often have a plant identification service provided by staff botanists. Many of these will charge for the service although it may also be a membership benefit of a botanical garden’s ‘Friends’ organisation – one of the many good reasons to belong.

Your local nursery is also a good place to ask, although I do mean an independent plant nursery or garden centre, not your box chain store. Although big box stores that sell plants very occasionally have qualified horticulturists (like the clever and knowledgeable Clare in Sydney’s Terry Hills Bunnings), they don’t have a policy of employing people who know anything much about plants, so she’s a rarity.

Take advantage of trained horticulturists at flower and garden shows and plant fairs as many shows have a plant ID booth.

Garden clubs are a rich source of expert plant knowledge with many friendly and generous local experts on hand to help you ID your mystery plant. And while you’re there you will probably also pick up lots of other very useful tips and help for your garden.

Plant societies dedicated to specific groups of plants can also be very helpful, such as native plant societies, or those devoted to Mediterranean plants, fruit growing, alpine plants, succulents and cacti, bromeliads, orchids, tropical plants – there are dozens of groups covering pretty much every type of plant.

If you have lots of plants in your garden that you can’t identify, it’s a very worthwhile investment to pay for a local horticulturist to come and spend some time in your garden, telling you what you have and also how to grow them for best results.



Identifying plants using keys

As an amateur plant ID sleuth, plant keys will not be something you can use yourself but they are indispensable to a botanist making a formal plant identification. I’m fairly horticulturally knowledgeable and I find them extremely difficult. They’re based on a long series of either-or questions, so if it’s a ‘yes’ you might cascade down to the next question, but if it’s a ‘no’ you’re directed to another part of the plant key. Most will centre around the reproductive parts of the flower as the most important part of the ID process.

As the questions narrow down, the key will start to supply a genus (the first part of a plant’s botanical name) and then a species (the second part) name to complete the full botanical name. A strong hand lens, good observational skills and an understanding of botanical terms required.

KeyBase RBG Victoria

For Australian flora, KeyBase, has keys published by the Royal Botanic Gardens Victoria which will help you narrow down an identification to species level is your already know the genus. You can also buy printed keys or find some online at the Centre for Australian National Biodiversity Research.

To identify British wildflowers, try this key from the Botanical Society of Britain and Ireland. For USA plants, try Flora of North America.


And what of Keren’s plant? From a variety of sources, brains trusts and fellow plant sleuths, it was determined that it was not a Clerodendrum or in the Lamiaceae family, and narrowed down to an Acanthaceae plant, quite possibly either a Barleria or a Pseuderanthemum.

So what characteristics mean that it is probably NOT a Clerodendrum, despite its superficial resemblances? No smell from the crushed leaves; no long exserted (sticking out) stamens; buds not that typical ‘musical note’ shape; and no berry-like fruit.

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Catherine Stewart

About Catherine Stewart

Award-winning garden journalist, blogger and photographer; writer for garden magazines and co-author of 'Waterwise Gardening'; landscape designer turned landscape design judge and critic; compulsive networker and lover of generally putting fingers in lots of pies. Particularly mud pies. Original creator of GardenDrum. South Coast NSW.

5 thoughts on “How to identify a mystery plant

  1. Hello Catherine

    I consider the mystery plant is Ruttyaruspolia ‘Phyllis van Heeden’ from Zimbabwe – believed to be a natural hybrid between Ruspolia and Ruttya. Not to common in Australia, but widely planted in warmer parts of Africa, Asia and the Americas. So yes you’re right, definitely from the Acanthaceae.

    When I saw the image I got exited as I thought you might be growing it in Sydney and know a source. I seem to remember seeing it growing in Cairns a while back, so I’ll have to look for it next time I’m up there. Its a tough plant and generally quite showy. I suspect the plant in the photos is in a little too much shade, needs a prune and a good feed. Generally plants are more compact and covered in flowers.


    • Arno I think you get the cigar! And what a sneaky plant – a hybrid between two genera. It goes to prove what a resource the web is and that if you just show the plant to enough people someone will recognise it and even know a local example! Well done! Jennifer

  2. Great article Catherine.
    I am glad that the mystery was solved. Having had a look at all the plants mentioned it just shows the difference between a healthy looking plant and one that clearly needs a little love.

  3. This is a fascinating article Catherine, thanks. I’m often on the prowl for plant names to tag my photos so when I need a picture of this or that I can easily search my database.

    Google images is good if you can think like the search engine when entering search terms. I’ve been pretty lucky with using that as a reference source but a trap is when someone names a plant incorrectly and then that photo is repeated on, eg, Pintrest, etc with the wrong name so the search throws up multiple examples of the plant with name x when in fact they’ve all stemmed (ahem, pun) from the same incorrect source.

    Books are still useful tools and I have a couple of shelves of handy reference volumes of all sorts. The ‘Field Guide to New Zealand’s Native Trees’ (Dawson & Lucas, 2012) is invaluable, even noting regional variations.

    On my recent trip to North America I purchased wildflower guides in Alaska and Washington state and read and learned as I went.

    I’m not a botanist but love learning about plants, their habitats, history and uses. Nature is endlessly fascinating.

    • Oh yes, the repeated wrongly-named plant will drive you crazy! As does a reference to that plant on a page but the photo is actually of another plant also discussed. If the photo file itself is not named and captioned then google image search will link any plant name in the text to it.
      And thanks so much for that NZ tree reference.

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