🌸 Diplacus

What it looks like

Diplacus is a genus of flowering plants in the lopseed family (Phrymaceae), traditionally placed in the figwort family (Scrophulariaceae), and the first thing to know about it is that most gardeners met it under a different name — twice. Thomas Nuttall described Diplacus in 1838 from western American material, but by 1905 most of its members had been sunk into the catch-all genus Mimulus, where they remained for more than a century, so generations of botanists and gardeners knew these plants only as monkeyflowers, Mimulus this and Mimulus that. Then DNA evidence intervened: a 2012 restructuring by Barker and colleagues showed that Mimulus in the old, broad sense was polyphyletic — a filing cabinet, not a family — and split it apart. Seven species stayed in a narrowly redefined Mimulus, 111 went to Erythranthe, and 46 went back to Diplacus, with a handful to smaller genera. Modern checklists count 49 accepted Diplacus species, native to the western United States and northwestern Mexico, most preferring dry and rocky areas. The name came home; the plants never left.

What a Diplacus looks like is a woody western shrub with a face. The genus holds the shrubby, sessile-flowered monkeyflowers: erect and woody in growth habit, often resinous or sticky-leaved, with tubular, two-lipped flowers in orange, red, pink, yellow, or white by species, the lower lip spotted or marked like a little face — which is where the old Mimulus name came from, Latin mimus, a comic actor or mime, for a flower that looks back at you. The technical characters that hold Diplacus together are parietal placentation in the ovary and sessile (stalkless) flowers, as against Erythranthe’s axile placentation and long pedicels — a distinction invisible to a gardener admiring the flowers and decisive to a taxonomist sorting the genera. Ecologically the split is visible too: Diplacus species like dry, rocky slopes, often in almost solid rock with very little moisture even on south-facing slopes, and will go summer-deciduous under drought stress, while the narrow Mimulus species like moist riparian ground and are not very drought tolerant. Sticky monkeyflower (Diplacus aurantiacus, long known as Mimulus aurantiacus) is the type specimen of the group: a small, resinous evergreen shrub of chaparral, coastal scrub, and open woodlands from southwestern Oregon through most of California, 2 to 3 feet tall by as wide, with deep green, sticky, lance-shaped leaves.

The butterfly context for this genus is the Variable Checkerspot guide, which lists, in its Host plants section, a famously broad menu: paintbrush (Castilleja), penstemon, besseya and figwort (Scrophularia) in the figwort clan; snowberry and honeysuckle in the honeysuckle clan; plus monkeyflower (Diplacus), plantain, and plants from several other families, all sharing bitter iridoid compounds the caterpillars sequester. That is a genus-level host entry — Diplacus named bare, as a genus, with no single species singled out — and it fits the butterfly: a checkerspot whose whole strategy is eating bitter plants and wearing the bitterness as defence. A genus guide is the honest unit for that mention, and this guide claims Diplacus species as a genus only.

One plain-text disambiguation, because the monkeyflower name covers three genera now and this genus guide must not swallow the other two. Mimulus in its modern, narrow sense holds only a handful of species — the moist-ground, herbaceous monkeyflowers — and it has no plant-guides genus guide of its own; no Mimulus guide exists on this site at all, and no monkeyflower guide exists either, which is why this Diplacus guide is not a duplicate of anything. Erythranthe holds the bulk of the remaining American monkeyflowers, 111 species with axile placentation and long pedicels, and it is not covered here either. Many nurseries, older field guides, and regional lists still use the Mimulus combinations — Mimulus aurantiacus for what is now Diplacus aurantiacus, Mimulus parryi for Diplacus parryi — and both names refer to the same plants. Buy by Latin name, check whether the label says Diplacus, Mimulus, or Erythranthe, and let this guide be the map of Diplacus, not a substitute for either of its former housemates.

How to grow

Growing Diplacus starts with accepting what kind of plant it is: a dry-slope western shrub, not a bedding annual. The genus pattern is full sun to part shade, in well-drained, lean, rocky soil, in a position on a slope or a raised bed where water passes through — the kind of ground where a monkeyflower can be found growing in almost solid rock with very little moisture even on a south-facing slope. Sticky monkeyflower wants that dry, sunny, chaparral address and will go summer-deciduous under drought stress rather than die, resprouting when water returns; fire-adapted members of the genus germinate after heat or smoke and resprout from basal growth after fire. What Diplacus does not want is a wet, rich, humid bed: that is Mimulus country, moist riparian ground, and a Diplacus planted there will rot where a Mimulus would thrive. The ecological split is the planting advice.

Propagation follows the woody-shrub pattern: seed, sown where the plant is to grow or started and transplanted young, and cuttings, which root well for the shrubby species. Give seedlings full sun and sharp drainage from the start, and do not overfeed: lean, rocky soil produces the compact, resinous, heavily flowering shrub the genus is, while rich soil produces soft growth that flops. If you are growing Diplacus for butterflies, the planting logic is the checkerspot’s logic — a woody monkeyflower in dry, sunny ground, near paintbrush and penstemon if you have them, left unsprayed, because the caterpillars are the point and a sprayed monkeyflower is a caterpillar trap, not a host plant. Hummingbirds and bees work the flowers too; the genus is highly specialised for their pollination, with abundant nectar and showy flowers opening sequentially along the stem.

Florida note, stated plainly: Diplacus is not a Florida genus. Its species are western plants of dry, rocky slopes, chaparral, and coastal scrub from Oregon to Baja California, and a Florida garden — humid, flat, and sandy — is the wrong address for them. Florida gardeners who want the same job done — tubular, hummingbird-visited flowers for a dry, sunny spot — should plant the tubular-flowered natives of their own region instead, and leave the bush monkeyflowers to the western slopes they belong to. A genus guide that pretended otherwise would be selling a map of the wrong territory.

Water & feeding

Water, for Diplacus, is a question of restraint. These are plants of dry, rocky slopes that survive drought by going summer-deciduous, and their roots expect soil that dries between waterings. In a genuinely sunny, well-drained site with normal rainfall for their region, established plants largely water themselves; in a wet summer or a heavy clay bed they sulk, rot, or simply fail to thrive, because the one thing a dry-slope shrub cannot forgive is wet feet. Water deeply but infrequently while plants establish, then back off — a plant that drops its leaves in a drought is not dying, it is doing exactly what it evolved to do, and a gardener who waters it back into leaf in August will undo a survival strategy with kindness.

Feeding: modest, across the genus. Diplacus grows in lean, rocky soils in the wild, and a spring topdressing of compost is the right scale of feeding — not a heavy fertiliser program, which mostly produces soft, leggy growth that flops and flowers poorly. The soil science here is the chaparral story: in dry, rocky, nutrient-poor soils, the plants that succeed are the ones that do a lot with a little, storing energy in woody stems and lignotubers and spending it in one flowering push, then resting through the dry season. A Diplacus’s roots live in that economy, and its yearly leaf fall returns what little it took. Plant it lean, water it sparingly, and let the woody base do the budgeting.

Common problems

• Wrong climate, wrong plant. The most consequential problem in the genus. Diplacus is a western dry-slope genus; humid, wet, or deeply shaded ground is a plant out of place. Check the species’ native range before you buy, and do not try it in Florida.
• Overwatering. Soggy soil rots dry-slope shrubs fast. Drainage matters as much as moisture, and a slope or a raised bed beats a flat, heavy bed every time.
• Overfeeding. Rich soil makes leggy, floppy plants that flower poorly. Lean, rocky soil is not neglect here; it is the habitat.
• Genus confusion with Mimulus and Erythranthe. The three genera spent a century filed together and still share nurseries, field guides, and old labels. Check the label — Diplacus for the woody, sessile-flowered shrubs — and buy by Latin name.
• Summer leaf drop mistaken for death. Diplacus species often go summer-deciduous under drought stress. A leafless shrub in August with live woody stems is resting, not dead; water it back only if you want to break its dormancy on purpose.
• Caterpillar nibbling. Checkerspot caterpillars may chew leaves, and that is the point of planting a host plant. A healthy shrub recovers, so do not spray the caterpillars — they are the crop.

Harvest

Diplacus’s harvest is seed, cuttings, and butterfly- and hummingbird-watching, in that order, and with no food or medicinal claims attached, because none is documented for this genus in the sources this guide draws on and inventing one would be exactly the kind of padding this library refuses. If you want seed, collect the capsules as they ripen and dry, and sow fresh or store dry; monkeyflowers recruit readily in open, rocky ground, and a gardener with one healthy shrub can soon have a drift. If you want more plants, take cuttings of the woody species, which root well, and transplant young plants into lean, well-drained ground in full sun.

The simplest harvest, though, is a dry-slope afternoon with no agenda at all: tubular flowers with faces like little actors, a hummingbird working the stem from bottom to top, a checkerspot caterpillar somewhere in the bitter leaves, and the knowledge that the shrub at your feet spent a century filed under the wrong genus and came back with its own name intact. Leave most plants standing through the season for the caterpillars, let a few capsules ripen for next year’s shrubs, and let the monkeyflowers do what they have always done — grow woody on dry rock, flower like actors, and feed the butterflies that know where to look.

Saving seeds

Diplacus seed is tiny, abundant, and gloriously impatient to escape, which makes saving it equal parts easy and fiddly. After flowering, each bloom leaves behind a small, dry capsule, and that capsule is your target. Wait until the capsules are dry and brown on the plant and beginning to split, then snip whole stems into a paper bag on a dry day. Do not wait for every capsule to be perfectly ripe at once: diplacus ripens in waves, and the earliest capsules will have already scattered their seed to the wind, and to your garden paths, if you hold out for a single tidy harvest. Several small collections beat one late one.

Back indoors, let the stems dry a few more days with good airflow, then shake and crumble them over a bowl or a fine sieve. What falls out will be dust-fine seed mixed with chaff, and that is normal. You do not need to separate every speck; winnow the lightest chaff away gently, pick out the larger bits of stem, and accept a little chaff in the packet. The seed itself should be dry and free of mould before storage, and anything damp or musty goes in the compost, not the jar. Label the packet immediately, with genus, species or cultivar if you know it, and year, because diplacus seed all looks alike and next spring you will not remember which packet was which. Trust me on this one.

Store cool, dark, and dry, in a paper envelope inside a sealed jar with a small desiccant packet if you garden in Florida, where humidity infiltrates every drawer and seed packet left to its own devices. Sow within a year or two for the best germination; like many tiny wildflower seeds, diplacus seed does not improve with age, and older packets deserve a germination test before they carry a whole sowing. When you sow, surface sow or cover only with the thinnest dusting of mix: these seeds need light to germinate, and burying them is the most common way to fail with them. Keep the surface evenly moist, never waterlogged, give them bright light and warmth, and expect seedlings in a few weeks, sometimes sooner in warm conditions. Fall sowing outdoors also works well for many species, letting winter do the conditioning and spring do the waking.

Now the trueness-to-type talk, because diplacus is where it really matters. Species grown on their own, with no close relatives flowering nearby, generally come true from seed, and that is how wild populations renew themselves. But named cultivars, and especially the brightly coloured hybrid monkeyflowers sold in nurseries, will not reliably reproduce themselves from seed: their seedlings may revert, shift colour, or land somewhere between their parents. If you fell in love with one exact flower colour, take cuttings, which root readily and preserve that plant precisely. Use seed for species, for drifts, and for happy surprises, and use cuttings for clones. That division of labour, seed for adventure and cuttings for fidelity, is the whole philosophy of diplacus propagation in one sentence, and it will save you from the heartbreak of raising a tray of seedlings that turn out to be the wrong shade of orange.

Species

Diplacus is a genus of 49 accepted species, and no guide can list them all, so this section names the species a North American gardener or butterfly-watcher is most likely to meet, in plain text, and states plainly that none is covered in particular by this genus guide. Sticky monkeyflower, also called bush monkeyflower (Diplacus aurantiacus, formerly Mimulus aurantiacus), is the small, resinous evergreen shrub of chaparral, coastal scrub, and open woodlands from southwestern Oregon through most of California. Red bush monkeyflower (Diplacus puniceus) is the red-flowered shrub of southern California. Diplacus parryi (formerly Mimulus parryi) is a further member of the genus. Diplacus glutinosus is the type species of the genus. Mimulus in its modern, narrow sense (seven species) and Erythranthe (111 species) are different genera that formerly shared the monkeyflower name; they are not covered here. This guide covers Diplacus species as a genus only.