You may have come across the terms "family" and "plant family" when reading about individual plants. Many gardening resources, including the Plant to Plate site, include this information. We mention it in every gardening facts article.
What is a plant family? Why does it matter? Read on to find out.
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What is a Plant Family?
Put simply, a family is one of the levels in the current taxonomic system. The taxonomic system classifies all living things.
The order of this system is as follows: domain, kingdom, phylum (also called division), class, order, family, genus, species.
Genus and species come from this same classification system, and they form the botanical names for individual plant types or species. For example, the botanical name for peppermint is Mentha piperita. In this name, Mentha is the genus, and piperita is the species.
A species is the most specific level of this classification. Continuing with the peppermint example, there are other plants in the Mentha genus such as spearmint (Mentha spicata) and pennyroyal (Mentha pulegium). Spearmint and pennyroyal are both close relatives of peppermint, but they are definitely different plants with separate characteristics.
A family is the next level up from genus. Two plants that are of the same family but different genera (plural of genus) will still share some characteristics. But they will have fewer things in common than 2 plants of the same genus.
Keeping with the peppermint example, peppermint and rosemary (Salvia rosmarinus) are both in the Lamiaceae (mint) family. They share some growth habits such as having a square stem and simple, opposite/whorled leaves, among other shared characteristics. But rosemary does not spread as aggressively as peppermint, and the 2 plants have very different watering needs, with rosemary preferring a dryer environment than peppermint does.
Some plant families have common names such as Brassicas (Brassicaceae family), legumes (Fabaceae family), and alliums (Alliaceae family). Others are referred to by common names such as "the mint family" (Lamiaceae) or "the daisy family" (Asteraceae).
So how does knowing which family a plant belongs to help gardeners?
Why It Matters
This statement appears on many of the family pages on the Plant to Plate website: "Knowing which family a plant belongs to can help you make decisions about crop rotation, companion planting, and other aspects of garden planning."
Let's break that down further.
Crop Rotation
Plants in the same family can attract the same pests. For example, onion thrips and onion flies/maggots are common in alliums (Alliaceae family), and these pests may invade and reproduce in the soil. So if plants from the same family are planted in the same spot the next growing season, the pests may become even worse.
On the other hand, if plants from a different family are planted next, this will not be a problem. If proper crop rotation is followed, the pests should not be present in the soil anymore by the next time plants from the original family are planted.
Similarly, plants from the same family often share similar feeding habits. For example, many plants in the Solanaceae (nightshade) family are heavy nitrogen and phosphorus feeders. So if you planted tomatoes in the same place every year (or tomatoes followed by bell peppers or another nightshade plant), the soil would quickly become depleted of nitrogen. On the other hand, planting a nitrogen-fixing plant such as something from the Fabaceae family would replenish some of that nitrogen and make the available soil nutrients more evenly balanced, especially when combined with other beneficial practices like soil amending.
Companion Planting
Issues like pests and nutrient requirements, mentioned above, can also factor into companion planting considerations. Different families can even out the nutrients taken from or added to the soil. This is the case in back-to-back seasons, as with crop rotations, but it can also be the case in the same season with companion planting.
On the other hand, some plant families should not be planted near each other due to attracting the same pests. See our Cucurbitaceae family page here for an example. Curcurbits can attract onion thrips, which can damage alliums, so the 2 families are best planted away from each other.
Check out our Companion Planting Basics article here for more information.
Other Aspects of Garden Planning
A plant's family can influence garden planning in other ways as well. For example, our carrot family page notes that members of this family should not be planted near each other since they can cross-pollinate and since they compete for the same nutrients. Both of these situations have negative impacts on the plants.
Speaking of garden planning, why not grab a FREE printable garden planner?
Knowing which family a plant belongs to can also give you clues about its edibility and best treatment, whether you are gardening or foraging. For example, for plants in the Brassicaceae (cabbage) family, the entire plant is edible. On the other hand, edible plants in the Apiaceae and Solanaceae families have toxic lookalikes, so they are best treated with extra care.
Where to Find Information on Plant Families
Each of our gardening facts articles considers a specific plant. For example, the gardening facts article Growing Lettuce: Quick Facts gives an overview of optimal growing conditions for lettuce in a straightforward, easy-to-reference format.
The first section of any of these gardening facts articles discusses the plant's family and close relatives. It also gives the botanical name for the plant — that is, its genus and species, as described above. You can also click on the family name or the common name to be taken the family page. You can try it on the lettuce page here. Clicking on the words "Asteraceae family" or "daisy family" will take you to the Asteraceae family page, where you can find more information on the family plus the plants in that family that we have already covered.
You can also access individual family pages by going to the gardening facts page and clicking the text that says "Family" in the "View by:" menu. Plant families are listed with both the family name and the common name in this section.
Some seed packets and seed websites will also contain this information.
Read More
Check out these articles about more of the categories listed on our gardening facts pages:
- How Often to Water Plants
- How Much Sun Does My Plant Need?
- Choosing the Right Planter for Your Container Garden
- Companion Planting Basics