“Mustard tree” is a name shared by two unrelated plants. One is the mustard of the gospel parable, a fast-growing herb that can tower over a person but is not a tree in the timber sense.1Grace Theological Journal. The Smallest Mustard Seed—Matthew 13:32 The other is a tough desert shrub whose leaves and twigs taste peppery like mustard and are best known as a natural toothbrush. Which one someone means depends on whether they are reading scripture or browsing a list of desert plants.
The Mustard of the Bible Parable
The gospels of Matthew, Mark and Luke tell of a tiny mustard seed that grows into a plant large enough for birds to rest in.2Genetic Resources and Crop Evolution. Reminiscences of the cultivated plants early days as treasured by ancient religious traditions: the mustard crop (Brassica spp. and Sinapis spp.) in earliest Christian and Islamic texts Early Christian and Islamic texts used mustard mainly as a symbol of small beginnings with large results.3Genetic Resources and Crop Evolution. Reminiscences of the cultivated plants early days as treasured by ancient religious traditions: the mustard crop (Brassica spp. and Sinapis spp.) in earliest Christian and Islamic texts It was also a familiar crop in the region, likely first domesticated by peoples ancestral to today’s Semitic speakers.4Genetic Resources and Crop Evolution. Reminiscences of the cultivated plants early days as treasured by ancient religious traditions: the mustard crop (Brassica spp. and Sinapis spp.) in earliest Christian and Islamic texts
The verse describes a garden herb that grows from a very small seed to tree size.5Grace Theological Journal. The Smallest Mustard Seed—Matthew 13:32 For centuries writers have proposed different plants as the scripture’s mustard tree without settling the question.6Journal of the Royal Asiatic Society. Art. VI.—On the Identification of the Mustard Tree of Scripture
A mustard herb can look surprisingly like a small tree. Black mustard can reach roughly 2 to 3 meters in a good season, and its stems thicken and branch widely by late summer. Small birds perch on it and feed among the seed heads. Unlike a real tree, though, it dies back every year.
Readers often ask about the “smallest seed” claim. Mustard seeds are only about 1 to 2 millimeters across, and they are not the smallest seeds of all plants; orchid seeds are far smaller. But among the garden seeds a farmer of the time sowed, mustard was famously tiny. The comparison fits everyday experience, not botany textbooks.
Some people say the parable meant Salvadora persica instead. It is a true woody plant that grows in the region, and its mustard-like taste earned it the mustard tree name. But a seed sown in a garden or field fits a crop herb better, so most scholars favor ordinary mustard.
Pinning down the exact species is hard. The gospels were written in Greek about a plant known in Aramaic or Hebrew settings, so the single word translated “mustard” could cover more than one mustard-family species. Several relatives grew in the region as crops or weeds, which makes black mustard the best-supported guess, not a proven identification. And because the parable is a teaching story, exaggerating the plant’s size was part of the point.
If you meet the phrase in a sermon or translation, note that English Bibles often say “tree” because the Greek uses a word for a larger plant. The wording alone does not mean a timber tree was intended.
Salvadora Persica, the Mustard Tree That Is Actually Woody
Salvadora persica is an evergreen shrub or small tree native to dry parts of Africa, the Middle East and South Asia. Its tissues contain mustard oil along with fluoride, silica, sulphur, vitamin C and resins.7Mutiara Medika: Jurnal Kedokteran Dan Kesehatan. MISWAK (Salvadora persica) as a Cleansing Teeth Chewing a leaf or twig gives the sharp, peppery bite of mustard. The plant’s chemistry includes the same sulphur compounds that give true mustards their heat, but the toothbrush tree is not a relative. True mustards belong to the cabbage family, which includes mustard, cabbage and canola and holds thousands of species.8TAXON. BrassiBase: Tools and biological resources to study characters and traits in the Brassicaceae—version 1.1 The shared name comes from flavor, not family ties.
The plant is usually a sprawling shrub, though it can become a small tree several meters tall. Its leaves are thick, slightly fleshy and pale green. Small greenish flowers are followed by small red to purple edible berries, and the twigs and roots are soft and fibrous.
Telling it from true mustard is easy once you know what to look for. Salvadora is woody and lives many years, while mustard is an annual herb. Mustard has bright yellow four-petal flowers, where Salvadora’s are tiny and greenish. Mustard makes slender seed pods; Salvadora makes berries. Mustard grows in fields, Salvadora in deserts and salty coasts. It is also called the toothbrush tree after its best-known use, and arak is a common Arabic name.
It grows in hot, dry places such as desert wadis, salty flats and coastal plains, often where little else survives. Elsewhere it is mostly seen in specialist nurseries, botanical gardens or as a potted curiosity.
The mustard flavor is strongest in fresh twigs and leaves, which is why people there chew them directly. The berries are edible and sweet-ish with a slight peppery note.
When buying one, check the Latin name, since a listing for “mustard tree” may mean Salvadora persica but common names alone can point to a different plant. It is usually sold as a small shrub or young tree in a pot, because it is slow to establish. If the listing mentions toothbrush use or arak, it is likely this plant, but the Latin name is the dependable check.
How the Toothbrush Tree Survives Salt and Drought
The toothbrush tree survives very salty conditions without lasting harm.9PubMed Central. Physiological, Anatomical and Metabolic Implications of Salt Tolerance in the Halophyte Salvadora persica under Hydroponic Culture Condition It moves salt into its leaves and locks it away inside swelling cells.10PubMed Central. Physiological, Anatomical and Metabolic Implications of Salt Tolerance in the Halophyte Salvadora persica under Hydroponic Culture Condition As a result, its leaves grow thicker and fleshier as the soil gets saltier.11PubMed Central. Physiological, Anatomical and Metabolic Implications of Salt Tolerance in the Halophyte Salvadora persica under Hydroponic Culture Condition It also grows fewer leaf pores in salty soil, so it loses less water.12PubMed Central. Physiological, Anatomical and Metabolic Implications of Salt Tolerance in the Halophyte Salvadora persica under Hydroponic Culture Condition
Storing salt inside swollen cells keeps it away from the parts of the cell doing the plant’s work. The trade-off is that fewer pores also limit how much carbon dioxide gets in, which is part of why the plant grows slowly.
In drought it slows its growth while keeping its leaves well watered.13PubMed. Regulation of ROS through proficient modulations of antioxidative defense system maintains the structural and functional integrity of photosynthetic apparatus and confers drought tolerance in the facultative halophyte Salvadora persica L. Slowing down saves energy until water returns, and after watering again it returned to normal growth within about 7 days.14PubMed. Regulation of ROS through proficient modulations of antioxidative defense system maintains the structural and functional integrity of photosynthetic apparatus and confers drought tolerance in the facultative halophyte Salvadora persica L. It also builds up sugars and acids that protect cells from drying out.15PubMed. Metabolomic study reveals key metabolic adjustments in the xerohalophyte Salvadora persica L. during adaptation to water deficit and subsequent recovery conditions That toughness is why it is considered a candidate for replanting degraded salty coastal land.16PubMed. Regulation of ROS through proficient modulations of antioxidative defense system maintains the structural and functional integrity of photosynthetic apparatus and confers drought tolerance in the facultative halophyte Salvadora persica L. A stalled plant that is watered again can start growing normally, so patience is better than replacing it quickly.
For a gardener, this means it suits hot, dry gardens and coastal sites with salty soil. It tolerates poor soil better than rich, wet soil, and overwatering is a bigger risk than drought. It is not frost hardy, so it suits warm climates or a pot brought indoors.
Miswak, the Chewing Stick From the Mustard Tree
A miswak is a twig or root piece from the toothbrush tree, chewed at one end until the fibers fan into bristles. Chewing immediately changes the makeup of saliva.17PubMed Central. A review of the therapeutic effects of using miswak (Salvadora Persica) on oral health Several studies found that a chewing stick cleans teeth as well as, and at times better than, a toothbrush.18PubMed Central. A review of the therapeutic effects of using miswak (Salvadora Persica) on oral health It scrubs mechanically and releases plant chemicals at the same time.19PubMed Central. A review of the therapeutic effects of using miswak (Salvadora Persica) on oral health
Studies report that the chewing stick reduces plaque and gum inflammation and helps fight tooth decay.20PubMed Central. Salvadora persica L.: Toothbrush tree with health benefits and industrial applications – An updated evidence-based review It has also shown antibacterial and antifungal effects.21PubMed Central. A review of the therapeutic effects of using miswak (Salvadora Persica) on oral health Many other claimed benefits, such as for diabetes or depression, come from lab experiments only.22PubMed Central. Salvadora persica L.: Toothbrush tree with health benefits and industrial applications – An updated evidence-based review
To use one, peel or cut back about 1 centimeter of bark. Chew the tip until bristles form, then brush along the gums and teeth. Trim the used tip every day or two to expose fresh fibers, store the stick dry, and replace it when it dries out.
A fresh, flexible twig about as thick as a pencil is easier to chew than an old, dried-out one. Dry sticks can be softened by soaking the tip in water before chewing.
It can be used with or between toothbrush sessions, but it does not replace dental checkups. Toothpaste with fluoride gives stronger decay protection than the stick’s natural fluoride. Brushing too hard with a stick, like with any brush, can irritate gums, so a gentle motion is the safer way.
Black Mustard as a Garden Weed
Black mustard is considered invasive in California.23TreePeople. If you can’t beat it, eat it! Five ways to use invasive black mustard Its tissues release chemicals that stop seeds of other plants sprouting and shorten their roots.24PubMed. Allelopathic effects of native and invasive Brassica nigra do not support the novel-weapons hypothesis It also damages helpful root fungi in the soil, cutting native plant growth by about a third in invaded fields.25PubMed Central. The invasive plant, Brassica nigra, degrades local mycorrhizas across a wide geographical landscape Native plants can therefore struggle in a patch even after the mustard is removed.
The weed spreads easily. Black mustard makes a huge number of small seeds, so a few plants can seed a whole hillside in one year. Seeds can sit dormant in soil and sprout when conditions are right, so a bare patch can fill in again later. It also sprouts early and grows tall quickly, shading out slower native seedlings.
Tall mustard stands can still shelter wildlife, including nesting blackbird colonies.26California Department of Fish and Wildlife. Detection, Monitoring, and Fates of Tricolored Blackbird Colonies in California in 2016 Grazing or cutting during nesting can destroy such colonies,27California Department of Fish and Wildlife. Detection, Monitoring, and Fates of Tricolored Blackbird Colonies in California in 2016 so where birds use the stand, clear mustard outside the spring nesting season. The young leaves and seeds are edible, so pulled plants can be eaten.28TreePeople. If you can’t beat it, eat it! Five ways to use invasive black mustard
To remove it, pull plants before they flower so they cannot seed. Seeds last in soil for years, so expect to pull repeatedly. Replant natives quickly to cover bare ground, and avoid composting plants that carry seed.
Its status varies by region, so check with a local extension office or native plant society about how to handle it. Where it is not listed as invasive, a few plants in a vegetable bed are mostly a nuisance and can be eaten. If you are unsure of the plant’s identity, wait for flowers: yellow four-petaled blooms point to a mustard-family plant, though many relatives look alike, so check leaves and pods too.
Growing Mustard From Seed
Mustard passes through eight stages: germination, leaf growth, stem lengthening, budding, flowering, pod formation, ripening and dying back.29Sask Mustard. Growth Stages of Mustard A well-grown plant can carry over 70 seed pods, each with about 23 seeds,30PubMed Central. Optimizing cultivation practices to enhance growth and yield of Indian mustard so one seed can give well over a thousand more.
For a home grower, germination shows as a pair of small round seed leaves, usually within days of sowing in warm, moist soil. Stem lengthening is when the plant bolts upward, signaling the shift from leafy growth to flowering. Pods start green and slender after the yellow flowers drop, and they dry to brown as the seeds ripen.
To sow mustard at home, plant in cool spring or autumn weather in full sun. Seeds sprout in days, and plants bolt to flower in summer heat. Pick leaves young for greens, and harvest pods when they turn brown, before they split.
Mustard seeds hold compounds called glucosinolates.31Journal of Food Composition and Analysis. Sinigrin and sinalbin quantification in mustard seed using high performance liquid chromatography–time-of-flight mass spectrometry Crushed and wet, they turn into the sharp-tasting compounds that flavor mustard.32Journal of Food Composition and Analysis. Sinigrin and sinalbin quantification in mustard seed using high performance liquid chromatography–time-of-flight mass spectrometry The sharpness appears only when the seed is crushed and mixed with water, which is why a whole dry seed has little smell.