Rock Flower Anemone Care: Phymanthus spp.

Rock flower anemones stand out from other sea anemones in the structure of their disc. Rather than bringing tentacles all the way to the mouth, the oral disc remains barren. The tentacles stay on the outer fringe – and there are around 200 of them! They’re short and feature small ridges that make them look beaded. (That’s where that other common name of beaded anemone comes from)

The center of the disc and the tentacles typically aren’t the same color. Even if you look at the “standard” reds, oranges, or purples, you get a two-toned invertebrate. It’s a look reminiscent of a sunflower. Assuming sunflowers came in every color of the rainbow.

Even wild rock flowers dazzle with their color displays. But the popularity of the group prompted selective breeding. Now you can find designer varieties that verge into downright exotic. Some even fluoresce under black light. These are known as ultra rock flower anemones. And they fetch some of the highest prices. But they look the brightest in a reef tank – as you can see in the YouTube video below:

Rock flower anemones bury all but that oral disc in the sand. It leaves the “flower” front and center. And it makes for the best view as the tentacles wave in the current. In the absence of a soft substrate, they WILL attach to rock, but it’s not the first choice for this vertebrate.

As with all sea anemones, rock flower tentacles possess nematocysts (stinging cells). It’s their primary means of defense. And, of course, it’s one of the ways they obtain their meals. The cells can lead to a skin reaction in humans, as well. If you plan to work in your tank and have rock flower anemones, make sure you wear gloves. You don’t want to risk that reaction turning severe when your little flower decides to defend itself.

Rock flower anemones belong to the Phymathidae family. And there are eleven species within the family:

• Phymanthus buitendijki (Borneman anemone)
• Phymanthus coeruleus
• Phymanthus crucifer (Red beaded anemone)
• Phymanthus laevis
• Phymanthus loligo
• Phymanthus muscosus
• Phymanthus pinnulatum
• Phymanthus pulcher
• Phymanthus rhizophorae
• Phymanthus sansibaricus
• Phymanthus strandesi

Rock Flower anemones show up throughout the tropical Caribbean. They’re common features on the sand and even up onto the rocks. You’ll see the tentacles and oral discs along the margins of reefs, usually in the shadier parts of the drop-offs.

Of course, if you get too close, they perceive that as a threat. Then those tentacles retract, and they close up.

The more nutrients a rock flower consumes, the faster they grow and the longer they survive. In the wild, this happens at a higher rate than in captivity. And that translates to lifespans of HUNDREDS of years! You probably won’t see that in your reef tank. However, with proper care and management, it’s not unreasonable to expect up to 80 years. (Not shabby for an invertebrate!)

In the Caribbean, you’ll spot a rock flower anemone buried in the sand. Or they might secure themselves on the vertical slope of rock along the outer barrier of the reef. They don’t stay near the surface where the sun’s intensity remains the highest. Instead, they go lower: around 10-100 feet (1-30m). The shaded regions of the tropical waters protect them from getting “burned.”

And mimicking that natural habitat? It’s relatively easy. They’re not the pickiest sea anemones in the world. You can get away with a sand bed OR make sure there’s a rocky structure available for them to attach to. Either way, the rock flower will settle in and make itself comfortable. (Ideally, though, they prefer to bury themselves in the sand)

They’re not as fussy when it comes to water movement – provided you offer SOME current. They need those tentacles to drift around. Again, moderate works best. And if you can set your powerheads to a varied pattern, they’ll love you. (Assuming sea anemones feel love, anyway)

Rock Flower Anemone Tank Size

Rock flower anemones can grow up to 8 inches (20.3cm) in diameter in the wild. However, in the average aquarium setting, they usually top out around 4 inches (10.2cm). This means they’re ideal in nano or even pico tanks. (Assuming you don’t get carried away and develop an obsession with collecting them like this hobbyist:)

A 5-gallon (19L) tank is plenty to keep your rock flower anemone happy. Well, provided you’ve set it up correctly. Those tentacles aren’t long, and the group doesn’t feel a need to wander around. So you’re in the clear on creating a modest display where you can enjoy those colors wherever you want.

Are Rock Flower Anemones Reef-Safe?

All sea anemones possess those nematocysts. And rock flower anemones are no exception. Depending on the species, a sea anemone can pose a potential threat to coral – especially if they wander around an aquarium. But rock flowers prefer to stay in one place. And they lack the long, stretchy tentacles you see in other sea anemones.

So you should be fine, right?

Right. Rock flower anemones don’t hassle their neighbors. You won’t see problems developing as long as you observe a healthy border between the anemone and any corals. All you need is a defined border of rock and sand, and your SPS corals won’t see a single sting.

You can also cluster different rock flowers together. They’re “friendly” with each other and won’t “argue” over space. It’s how many aquarists create dynamic displays, adding clusters of color throughout their tanks.

Rock Flower Anemone Diet

While rock flower anemones put people in mind of gorgeous bouquets (or the flowers from Alice in Wonderland), they drop the plant act when it’s time for dinner. These invertebrates are complete carnivores. Those 200 tentacles serve to lure in, capture, and hold prey items so the mouth can devour them. And it’s your job to make sure they get the nutrition they need.

Unlike corals – or actual flowers – you can’t expect your rock flowers to survive on photosynthesis. You need to provide meaty options if you want the anemone to stay healthy. Look at the size of the opening in the disc and then chop these proteins into appropriate pieces:

If you’re not careful about the size of your chopping, your rock flower anemone won’t be able to eat or digest the food. Then they won’t grow. Not to mention the whole starvation thing. (Though they’ll probably migrate in search of food first)

You should also consider mixing in your vitamin supplement of choice. And rock flower anemones benefit from the addition of highly unsaturated fatty acids (HUFA). The better the quality of their food? The more they’ll grow.

In general, sea anemones tend to wander. When they don’t like the conditions where they’re living, they pick up and move on. Rock flower anemones can do the same thing, but they choose not to. They’re one of the more sedentary groups out there. Burying themselves in the sand is their M.O. It’s one of the reasons their ideal for beginners. You don’t need to worry about implementing protective measures around the tank.

More problematic are the other invertebrates you usually find in a reef tank. Sea stars maneuver their tube feet around those short rock flower tentacles to get their meal. And nudibranchs have no problem coping with stings. Before you know it, your tank doesn’t have a single rock flower left.

The other mistake hobbyists make is introducing clownfish. Yes, clownfish and sea anemones mix – usually. But rock flower anemones come from the Caribbean. Clownfish? Yeah, they don’t. There’s absolutely NO compatibility between the two species. The more likely result if you attempt the experiment is a dead clownfish. Your rock flower will sting and EAT poor Nemo.

If you want to witness that symbiotic relationship, pick species that share the native region with rock flowers:

One of the best things about the rock flower anemone? No two look alike. Of course, that makes attempting to tell a male and female apart tricky. Good thing the group can reproduce via sexual OR asexual methods.

For sexual reproduction, the males and females spawn in autumn. They release the gametes into the water column. The fertilized eggs hatch a granula larva. The granula sinks to the bottom and finds a rock to attach to. It then develops into a polyp that continues to grow.

You can also see asexual reproduction. The base will divide, producing a second oral disc. It’s similar to the budding you see with coral species. The growth is usually SLOW, and it could take weeks before the new rock flower separates.

The success and growth rate depends on the amount of food available to your rock flower anemone with either reproductive method. Obviously, they need resources. But a healthy organism is more likely to reproduce than an emaciated one. Providing a quality diet will up your odds of success.

Rock flower anemones appear to check all of the boxes you could want. They’re not demanding in their care, they come in bright colors, and they’re not difficult to feed. What more do you need? Well, as with any species, you still find some quirks you want to keep in mind.

Pros

• Rock flower anemones are reef-safe, rarely moving around the tank or crossing sand-rock barriers to sting corals.
• You can set up rock flowers in nano or even pico tanks.
• Rock flower anemones tolerate sharing a tank with most popular fish species.

Cons

• You need to drip acclimate your rock flower anemone due to the stress of shipment, or it may not adapt to the tank.
• Rock flowers are NOT compatible with clownfish. They’ll sting and possibly eat the fish.
• Rock flower anemones don’t have set growth rates; it’s dependent on the amount of food they receive.

Collecting rock flower anemones tends to get addictive. Every time you see a new color variety, you need to get it. It’s not the worst problem in the world, considering how easy they are to care for. So why not learn a little more – just in case you need more convincing?

This YouTube video goes through everything you need to know about rock flower anemones:

Want to know about some of the best rock flower anemone tank mates?

Or would you like to explore some other gorgeous invertebrates?

Conclusions

Nothing looks quite as spectacular as a rock flower anemone. Well, except perhaps an entire tank of rock flowers. You can’t look away from the rainbow! And the ease of managing these sea anemones makes them accessible to anyone. They’re the perfect “gateway anemone.”

Just don’t blame me if you find yourself with a rock flower habit you need to support down the road.

References