Below the Caudex: The Genetics Gamble — What an Adenium Seedling Can (and Cannot) Tell You

By Michael White — American Adenium
30 Years of Cold-Climate Growing Experience

One of the most common mistakes I see people make with seed-grown Adenium happens surprisingly early.

A grower buys seed from a plant with a particular flower, caudex, branching habit, leaf shape, or overall appearance. The seeds germinate. A few months later, the seedlings don’t look exactly like the parent plant.

And the immediate conclusion is:

Something must be wrong.

Maybe the seeds were mislabeled. Maybe they aren’t the variety I purchased. Maybe the seller sent me the wrong seed.

Sometimes mistakes certainly happen.

But very often, what the grower is seeing is simply genetics doing exactly what genetics does.

And that brings us to something every person growing Adenium from seed should understand:

A seed is not a clone.

When you germinate an Adenium seed, you aren’t reproducing the mother plant. You are starting a new individual whose characteristics come from a genetic combination of its parents.

And you may not know what that individual is going to become for quite some time.

That uncertainty isn’t a weakness of growing Adenium from seed.

For many of us, it’s one of the most fascinating parts of it.

Let’s Start With the Mother Plant

When Adenium seeds are offered under the name of a particular cultivar or selection, growers naturally look at the mother plant and imagine that their seedlings will eventually look like it.

That’s understandable.

The mother plant is usually the plant we can identify with confidence. We can photograph it. We can observe its caudex. We can see its flowers, leaves, branching structure and growth habit.

But the seed developing on that plant contains more than the genetics of the mother.

There is also pollen involved.

That pollen contributes approximately half of the seedling’s nuclear genetic material.

If the pollination was carefully controlled and both parents are known, we have considerably more information about the cross.

If it was open-pollinated, the pollen parent may be unknown.

Either way, the resulting seedlings are genetically unique individuals.

Imagine standing five children from the same family next to one another.

They share parents. They share ancestry. You may immediately recognize family traits among them.

But they aren’t identical.

One may resemble the mother strongly.

Another may resemble the father.

Another may show characteristics from grandparents or earlier generations.

And another may possess a combination that doesn’t immediately remind you of anyone else.

Seed-grown Adenium behave much the same way.

A Seed Name Is Not a Promise of an Identical Plant

This distinction becomes especially important with named Adenium.

If you purchase a vegetatively propagated plant—a graft, for example—the scion is genetically the same selection from which that plant material originated.

Seed is different.

Suppose we have an exceptional Adenium arabicum with a massive caudex, compact branching and unusually dark foliage.

We collect seed from that plant.

Those seedlings have the mother plant’s genetics behind them.

But that does not mean every seedling will reproduce every visible characteristic of the mother.

One seedling might develop a particularly broad caudex.

Another might remain relatively tall.

One might branch early.

Another might be reluctant to branch.

One may inherit darker foliage.

Another may have ordinary green leaves.

And some seedlings may eventually develop into plants that are more interesting than either parent.

That last possibility is one of the reasons seed growing becomes addictive.

You’re watching genetic potential reveal itself one plant at a time.

Genetics Are Only Half of What You’re Looking At

Here’s where the subject becomes even more interesting.

When we look at an Adenium, we aren’t looking at genetics alone.

We’re looking at:

genetics × environment × time.

A seedling has genetic potential.

But how that potential is expressed can be influenced by growing conditions.

Light intensity matters.

Temperature matters.

Nutrition matters.

Root development matters.

Container size matters.

Watering practices matter.

Dormancy and seasonal growth cycles matter.

Pruning and training can matter.

And perhaps most importantly:

age matters.

A characteristic that isn’t obvious at six months may become much more pronounced at eighteen months, three years or five years.

This is particularly important with plants grown for structural characteristics such as Adenium arabicum.

Seedlings Change — Sometimes Dramatically

Young Adenium are unfinished plants.

That sounds obvious, but it’s remarkably easy to forget.

When we look at a six-month-old seedling, our minds naturally want to extrapolate:

“This is what this plant is going to look like.”

Not necessarily.

Adenium can undergo substantial changes as they mature.

Caudex proportions change.

Trunks thicken.

Branching patterns develop.

Internodes may change.

Leaf size and shape can change.

The relationship between the caudex and canopy changes.

Flowering introduces an entirely new group of characteristics we couldn’t evaluate when the plant was young.

And environmental changes can cause the same plant to look remarkably different from one season to another.

This is why I am very cautious about making absolute judgments about young seedlings.

A seedling isn’t necessarily showing you its final form.

It’s showing you where it is in its development right now.

Those are two very different things.

The Caudex Is a Perfect Example

Consider the caudex.

If you’re growing Adenium arabicum, you may be looking for a broad, powerful base and a compact bonsai-like structure.

So naturally, when seedlings are young, growers begin comparing them.

“This one is fat.”

“This one is skinny.”

“This one is taller.”

“This one isn’t developing like the mother plant.”

Those observations are useful.

But the conclusions can be premature.

Different seedlings can reach developmental milestones at different rates.

One plant may put substantial energy into above-ground growth early.

Another may thicken quickly.

A third may appear rather ordinary for its first year and then begin developing a much more impressive structure later.

The growing environment can amplify those differences.

So when I evaluate seedlings, I’m looking for tendencies—not demanding that a juvenile plant already resemble the mature specimen pictured on a seed listing.

Recessive Traits and Hidden Genetics

There’s another reason seedlings can surprise us.

Not every genetic characteristic expressed in a seedling was necessarily obvious in the parent plant.

Plants carry genetic information that may not be visibly expressed in the parent but can appear in offspring depending upon the genetic combination inherited from both parents.

This is one reason seedlings can occasionally display unexpected characteristics.

You may grow a group of seedlings from the same seed lot and notice one plant with an unusual leaf shape, growth pattern, pigmentation or structural characteristic.

That plant isn’t necessarily “wrong.”

It may be expressing genetic variation that its siblings aren’t expressing.

Plant breeders pay very close attention to these outliers.

Because occasionally, the unusual seedling is the important one.

Many horticultural selections begin exactly this way:

Someone grew a population of seedlings.

Most were ordinary.

One wasn’t.

And somebody noticed.

This Is Selection

Once you understand this, growing Adenium from seed begins to look very different.

You’re not simply germinating plants.

You’re growing a population.

Suppose I germinate 50 seeds from an interesting Adenium arabicum parent.

At first, I may simply be concerned with germination percentage and healthy establishment.

Later, differences begin appearing.

Some seedlings grow faster.

Some develop wider bases.

Some remain compact.

Some develop stronger branching.

Some display particularly attractive foliage.

Over time, I can begin selecting plants based upon the characteristics I value.

This is one of the fundamental processes behind plant breeding.

Grow. Observe. Compare. Select.

Then do it again.

The larger the population, the greater the opportunity to observe variation.

That’s one reason serious growers frequently germinate more seeds than they ultimately intend to keep.

They’re not necessarily trying to own fifty plants.

They’re looking for the exceptional plant among fifty seedlings.

What About Flower Color?

Flower expectations probably create more misunderstanding than almost anything else in seed-grown Adenium.

A spectacular flower on the mother plant does not guarantee that every seedling will produce the same flower.

Flower characteristics can segregate among seedlings.

Color can vary.

Pattern can vary.

Petal shape can vary.

Flower size can vary.

Single versus more complex flower forms may vary depending upon the genetics involved.

Even seedlings from carefully selected parents can produce a range of outcomes.

If you require an exact flower, vegetative propagation of the known cultivar is the more reliable route.

If you’re growing seed, you’re participating in a genetic lottery.

But “lottery” shouldn’t imply completely random.

Parentage matters.

Selection matters.

Breeding matters.

Good genetics can increase the probability of desirable outcomes.

They simply don’t guarantee that every seedling will be identical.

F1, F2 and Later Generations

You’ll sometimes see seed identified as F1, F2 or later generations.

These designations describe generations within a breeding line or cross.

An F1 generation is the first filial generation produced from the parental cross.

If members of that generation are crossed or selfed to produce another generation, we reach F2.

And something interesting often happens there.

Variation can become much more visible.

Traits that weren’t obvious in the first generation can segregate into different combinations.

For someone trying to produce absolutely uniform plants, that variation can be frustrating.

For someone selecting plants, it can be incredibly valuable.

Because variation gives us something to select from.

A breeder isn’t necessarily looking for fifty identical seedlings.

Sometimes the breeder is looking for one extraordinary seedling.

Provenance Still Matters

None of this means seed identity doesn’t matter.

Quite the opposite.

Knowing where seed came from is extremely valuable.

Parentage provides information about the genetic pool we’re working with.

A reputable seed source should make reasonable efforts to correctly identify seed and describe parentage accurately.

But we have to separate two ideas:

Genetic provenance and guaranteed phenotype are not the same thing.

Provenance tells us where the genetics came from.

Phenotype is what the individual plant ultimately becomes and expresses.

A seedling can be completely legitimate offspring from a particular mother plant while looking noticeably different from that mother.

That isn’t contradictory.

That’s sexual reproduction.

When Should You Start Evaluating Seedlings?

Immediately.

But don’t confuse evaluation with final judgment.

I evaluate seedlings from the moment they germinate.

I’m looking at vigor.

Stem thickness.

Internode spacing.

Leaf development.

Symmetry.

Root structure.

Caudex development.

Branching tendencies.

Response to environmental conditions.

But early observations are data points.

They aren’t necessarily verdicts.

As the plants mature, the information becomes more meaningful.

Think of it as watching a story unfold.

At three months, you’ve read the first few pages.

At one year, maybe you’ve finished several chapters.

When the plant begins developing mature structure and flowering, you’re finally getting much closer to understanding the whole character of the plant.

And even then, Adenium continue changing for years.

Don’t Throw Away the Ugly Duckling Too Quickly

This is something I’ve learned to appreciate after decades of growing plants.

Plants can surprise you.

The seedling you are most impressed with at six months isn’t always the plant you’re most impressed with three years later.

And the awkward plant you almost discarded can sometimes develop into something exceptional.

That doesn’t mean we should never cull seedlings.

Selection requires judgment.

Space is finite.

Resources are finite.

Weak or unhealthy plants shouldn’t necessarily consume growing space indefinitely.

But there’s a difference between identifying a genuinely poor plant and eliminating a healthy seedling simply because it hasn’t yet developed the characteristic you expected.

Give genetics enough time to express themselves.

Environment Can Hide Genetic Potential

This deserves special attention for those of us growing Adenium in climates very different from their native environments.

I grow Adenium in a cold climate.

That means my plants experience seasonal conditions that growers in Thailand, India, Vietnam or other tropical and subtropical regions may never encounter.

Our growing season changes.

Our light changes.

Temperatures change.

Indoor conditions change.

Growth slows.

Then spring arrives and the plants begin responding again.

If a seedling spends part of its development under less-than-ideal conditions, some of its genetic potential may not be immediately obvious.

That doesn’t mean the genetics disappeared.

It means phenotype is being influenced by environment.

Give that same plant strong light, appropriate root-zone temperatures, proper nutrition and a full growing season, and you may see a very different plant several months later.

This is one of the reasons I believe good cultivation and good genetics belong in the same conversation.

You can’t fairly evaluate genetics if the plant never receives the conditions necessary to express them.

Growing Seed Changes the Way You Look at Adenium

Once you really understand seed-grown variation, you stop looking at a tray of seedlings as twenty copies of one plant.

You begin looking at twenty possibilities.

That’s a completely different mindset.

You start noticing subtle differences.

Why is that seedling branching already?

Why is this one’s caudex spreading laterally?

Why does that plant have shorter internodes?

Why are those leaves darker?

Why is this plant growing differently even though every seedling in the tray receives essentially the same treatment?

Now you’re observing.

And observation is where growing becomes horticulture.

What I Want New Growers to Remember

If you purchase Adenium seed because you saw a beautiful mother plant, let that plant tell you something about the genetics behind the seed.

Don’t treat the photograph as a guaranteed picture of the plant you’re going to grow.

Your seedling is its own individual.

It may strongly resemble its mother.

It may express characteristics from the pollen parent.

It may show characteristics from earlier generations.

It may develop traits slowly.

It may surprise you.

And every once in a while, you may germinate something better than what you expected.

That’s the opportunity seed gives us that cloning never can.

A graft preserves something exceptional that already exists.

A seed gives us the opportunity to discover something exceptional that has never existed before.

And I think that’s one of the most exciting reasons to grow Adenium from seed.

So when your seedlings emerge, don’t rush to decide exactly what they are going to become.

Grow them well.

Pay attention.

Take notes.

Compare siblings.

Photograph their development.

Give them time.

Then watch what the genetics reveal.

Because sometimes the most interesting thing growing in your collection isn’t the mature plant you purchased.

It’s the six-month-old seedling sitting quietly in the corner that hasn’t shown you what it is yet.

Below the Caudex

Below the Caudex is an American Adenium series exploring the biology, cultivation, genetics and observations behind growing better Adenium.

Growing these plants successfully isn’t just about knowing what to do.

It’s about understanding why the plant responds the way it does.

And sometimes the answer is hiding below the caudex.