kcweeds

Learn to Identify Plants

If you’re looking at a new plant and not sure where to start with an ID, the internet is your friend! Whether you’re looking in a park, on a trail, or in your own backyard, we hope that these tips will help you figure out what plant you’re looking at. We’ll get into some plant ID specific applications, but before you get started it will be helpful to become familiar with some useful plant terms.

Key Features
Tools to Use
Ask an Expert
Photo Tips

Key Features

Click a topic heading below to learn more (dropdown box)

Life Cycle and growth pattern

Note: all bolded words are defined in order of their appearance in the respective photo galleries below each section.

The life cycle of a plant starts with germination, cotyledons sprout, and the cycle continues as it grows and reproduces, then ends when the plant dies.

germination: process of growing from a seed or spore. image of oval seeds on a table labeled giant hogweed, heracleum mantegazzianum
cotyledon: first leaves that emerge when seed germinates. image of a gloved hand and a small new plant growth, labeled: herb robert, geranium robertinum

An annual plant goes through the whole cycle in one year.

Biennial plants will do the same in two years. Typically, year one is germination and growing from a seedling into a rosette. Year two the rosette “bolts” and often grows much taller stalks which then flower, go to seed, and then die.

Perennials with their longer life cycles vary more. Generally speaking, herbaceous perennials “die” back every year during dormancy. Deciduous perennials lose their leaves, but trunks and stems remain. Finally, evergreen plants keep their foliage all year round.

Select the thumbnails on the bottom to navigate through images.

text: annual - one year life cycle. image: pink pea-like flowers on a stem with bright green leaves, labeled - policeman's helmet, impatiens glandulifera
text: biennial - two year lifecycle. image: 2 photos, left of a green leafy low growing plant labeled "1st year", right of a cluster of taller plants with yellow flowers at the top labeled "2nd year". plant labeled: tansy ragwort, Jacobaea vulgaris
text: rosette - circular cluster of leaves at ground level. image: low growing bright green wavy leaves on brown soil. labeled: tansy ragwort, jacobaea vulgaris
text: bolting - maturing and going to seed. image: bright green shrubby plant with kidney shaped leaves and an upright stem with smaller leaves. person in background in orange vest, labeled: garlic mustard, allaria petiolata
text: perennial - more than two-year life cycle. image: light yellow 5-petaled plants on greenery, labeled: sulfur cinquefoil - potentilla recta
text: deciduous - plant that loses leaves annually. image: bright green tree leaves with 5 leaflets fill the image, labeled: horse chestnut - Aesculus hippocastanum
text: evergreen - leaves remain green and functional for more than a single growing season. image: branch of tree with sharp looking dark green waxy leaves and red round berries. labeled: common holly, ilex aquifolium
Stem

The stem, the main structure of the plant can sometimes get lost behind the showier parts but don’t count them out as an identification feature. The color, pattern, features of the nodes, and other aspects can all narrow down a plant.

Words: Stem - main part of plant, supports leaves, flowers, and fruit. Image: smooth green stem with reddish purple splotches and streaks, labeled: poison hemlock, conium maculatum
text: node - growth point on a stem. image: close up of a thin woody tree with small new branches growing opposite of eachother in a "V" shape. labeled: noraway maple, acer platanoides

Photo of Norway maple by Rutger Barendse via Saxifraga

Leaves

Leaves are a useful feature to compare – below are some aspects to look for when learning a new plant.

Note: all bolded words below are defined in order of their appearance in the adjacent photo box.

text: simple leaf - leaf blade is undivided. image: green large waxy leaves labeled: cherry laurel, prunus laurocerasus
text: alternate - one growth per plant node, alternate sides of stem. image: branch with sharp dark green waxy leaves and red round berries, labeled: common holly, ilex aquifolium
text: compound leaf - leaf is divided, forming leaflets. image: tree branch with cluster of bright red berries at end, leaflets are matte olive green and face nose-to-nose along the stem.
text: opposite - growth from the same node, opposite sides of the stem. image: thin woody trunk with new reddish growth coming from opposite sides of the trunk, making "V" shape. labeled: norway maple, acer platanoides
text: whorl - at least 3 leaves at a node. image: dark green narrow leaves growing in a spiral around main stem, getting smaller towards the top. labeled: spurge laurel, daphne laureola.

Leaves can grow off the stem in various ways. For common holly, simple leaves grow directly off the stem in an alternate arrangement (leaves don’t grow nose-to-nose, take turns along stem). Pro tip: this is a good way to distinguish common holly from our native plant, Oregon grape! The spikey leaflets sometimes throw people off, but Oregon grape actually has compound leaf, similar to European mountain ash.

Other leaf arrangements are opposite (leaves grow nose-to-nose), and whorled (leaves grow in a spiral arrangement around the stem). Knowing a plants leaf arrangement can help you narrow down which plant family you are looking at.

text: margin - edges of a leaf, image: sharp jagged neon green leaflets, labeled: evergreen blackberry, rubus lacinatus
text: lobed - leaf margin has a pattern of rounded sections. image: light emerald green leaves with some red leaves against a fence, leaves are lobed (deep waves) and palmate. labeled: shiny geranium, geranium lucidium
text: toothy - leaf edge with small, jagged projections. image: 5 leaflets with serrated knife like edges, labeled: himalayan blackberry, rubus armeniacus

As we narrow in more on the leaves themselves, there’s many different features to compare across species. Here, I’ll simply direct your energy to the margins, or edges of the leaves. Are they rounded and lobed? or sharp and toothy? Start to note of the differences and you’ll be surprised you ever had them mixed up in the first place.

Photo of evergreen blackberry from WSNWCB. Photo of Norway maple by Rutger Barendse via Saxifraga.

Flower features

Flowers are typically fairly showy and are a common go to when trying to identify a plant. Color, size, and number and shape of the petals are all useful features to note.

text: flower a reproductive structure of plants, part of the plant that blossoms. image of a smiling noxious weed specialist holding a giant hogweed, Heracleum mantegazzianum, flower
petal a modified, often brightly colored, leaf, a part of the flower. image of sulfur cinquefoil, Potentilla recta, a yellow flower

When looking at very similar looking flowers, the number and shape of the bracts and sepals, both modified leaves with different evolutionary histories,

text: bract, small, modified leaves below the flower. image of sulfur cinquefoil, Potentilla recta, a yellow flower with small leaf life structures on the stem circled.
text: sepal, outer part of a flower that encloses a developing bud. image of sulfur cinquefoil, Potentilla recta, a yellow flower with a circle and an arrow pointing to a small leaf like structure just below the petals
Root System

The underground part of a plant can be just as useful for ID. It is certainly useful when considering control options. A root system can store lots of nutrients and energy. Ever wonder why simply cutting the plant down isn’t getting rid of it? See if it has a taproot or rhizomes, both of which can give the plant energy to respout.

text: root, underground plant structure for support and water and nutrient uptake

Photo of Himalayan blackberry rhizome from WSNWCB

Tools to Use

If you have a smartphone, it may have a built-in app that can help identify your weeds. There are several others you can download as well. Listed are a few of the team’s favorites. What apps do you like to use?

Pro Tip: If you aren’t confident about the ID, do an internet search! See if the images you find match up with what you are seeing.

  • A Community for Naturalists · iNaturalist
    • If you are a little more confident in your ID iNaturalist is a fantastic tool to track the distribution of noxious weeds. It can even help us in early detection rapid response (EDRR). Check out our blog post on an early spotting of floating primrose-willow.
  • Wildflower Search
    • Despite the name, this is useful for more than just wildflowers and unlike some of the others can be used offline.
  • If you know you’re looking at a noxious weed, you just aren’t sure which one, the Washington State Noxious Weed Control Board has a handy tool, similar to Washington Wildflower Seach where you can plug in key features, and it will give back a list of possibilities.

Ask an Expert

If the internet and apps just aren’t cutting it, try asking an expert! We may refer you to these groups ourselves if the plant in question is not a noxious weed so you can receive the best possible advice.

Master Gardeners of King County

The Extension Master Gardeners have clinics throughout King County, where people can go for FREE advice on gardening, plant problems, plant identification, pest management and soil improvement. You can find a list of locations here. You can also email us plant questions at ask-a-mastergardener@live.com . 

PNW Garden Hotline

The Garden Hotline offers individualized solutions to garden problems that are practical, safe, effective, and natural. Our services are FREE to home gardeners and landscape professionals throughout Seattle and King County. We are reachable through our website: The Garden Hotline | Pacific Northwest Garden Solutions or by calling 206-633-0224.

Or for all things noxious weeds, ask us! Our email is noxious.weeds@kingcounty.gov and the program phoneline is 206-477-WEED (9333). Our website is also a useful resource at kingcounty.gov/weeds and be sure to check out our Instagram. There’s always fresh content on weed identification, control, and more.

a field with multiple people all in orange vests using their phones to look closely at plants
Noxious weed specialists training seasonal crew members on how to use iNaturalist

Photography Tips

  • Send in close ups! Now that you know all those handy terms, you can let us know you’re looking at the leaf margin or you think it’s a first-year rosette. The more specific the photo the easier it is for us to identify the plant. Close ups of leaves, any reproductive parts (seeds, flowers, etc.), and the stem/stalk are all very helpful.
  • Multiple photos! The more angles the better.
  • Timing! Let us know when you took the photo, seasonality can really change what we look for in identification.
  • Location! Just like seasonality, habitat can be another key piece of the puzzle. If it is in a wetland vs a roadside, we may have a different answer for you.
  • Attach to the email! This allows us to zoom in on specific features without downloading the image.

Now that you have all these new tips and tricks in your back pocket, check out our summer weeds post! What features are you noticing on those weeds?

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