Streptocarpus Science

This page is for any interesting sciencey information about Streptocarpus.
  1. Flower anatomy
  2. Flower colour genes
  3. A master hybridiser's hybridising notes
  4. "Gesneriaceae - A Scientific Perspective"
1.  Streptocarpus flower anatomy - click on image for better view
This drawing is of one half of a flower. It is important to note that Streptocarpus flowers actually have two stamens (one on each half) that are loosely joined at the anther. Streptocarpus flowers have five petals.
2.  How do Streptocarpus colour genes work?
I borrowed this from the Streptocarpus Info forum pages.

Dr. Jeff Smith
Indiana Academy
Ball State University
Muncie, IN 47306

Flower Color Genes in Streptocarpus

During my work with the flower color genetics of African violets, I found several articles on the flower color genetics of Streptocarpus that were published in the 1950's by Lawrence and Sturgess. If you are hybridizing with Streptocarpus, I would urge you to read the original articles, but the following is a quick summary of their reports.

V = places pigment in the flower stems.
F = places pigment in the petal cells.
V and F are both necessary to give "color", but do not control "which color". These genes are similar to house keys that let a painter in the house, but they don't control what color he will paint the rooms. When V or F are recessive (vv or ff) the flowers will lack any color and will be white in appearance.

I = color intensity. II = intense color, Ii = medium color and ii = pale color.
This gene doesn't control "which color", just how "intense" the final color will be in appearance.

The actual flower color genes (O,R,D) are very similar to that of African violets, although the names given to the visible color are somewhat different. The names of the colors and their genotype codes are given below. Where the second copy of the gene is given as a "_", the second copy can be a dominant or a recessive. For example, in Blue flowers, only one dominant of each the three genes is needed.

Blue = O_R_D_
Magenta = ooR_D_
Pink = oorrD_
Mauve = O_R_dd
Rose = ooR_dd
Salmon = oorrdd

The Blue-Magenta-Pink series is the same as the Blue-Fuchsia-Pink series in African violets. The Mauve-Rose-Salmon series is the same as the Coral Blue-Coral Red-Coral Pink series in African violets.

Other genes affect the pattern of color or modify the final color. Some of these genes are:

B = gives a blotch of color in the throat of the bloom. The recessive "bb" produces flowers without a blotch. The trait appears to produce a darker or more intense version of the color of the outer edges of the petals. Thus, you can get dark pink blotches on a lighter pink flower etc.

H= gives color on the capitate hairs of the pistil. The recessive "hh" gives white or colorless hairs.

Genes F,I,B, and H are very closely linked and are usually inherited as a single unit. Therefore, many plants have pigmented flowers with at least medium intense color and blotches in the throat or have white flowers without blotches.

C = adds a co-pigment to the flower color. This gene modifies the appearance of the color, giving a bluish tint to the overall color. Plants with the recessive "cc" combination have flowers that are "brighter" in appearance. In the Mauve-Rose-Salmon series, the dominant gene produces undesirable murky colors.

L = puts nectar guides in the flower tubes. The recessive "ll" produces flowers without the lines.

Y = puts a yellow central stripe in the flower tube. I suspect that the size of the yellow area changes with "YY" versus "Yy" plants. The recessive "yy" would produce flowers with no yellow in the flower tube.

This is a beginning list. Other genes are mentioned in the original articles, but they appear to involve some rarely seen color modifications. Genes for plant size, fragrance etc. were not mentioned in these articles.


Lawrence, W.J.C. and V.C. Sturgess. 1957. Studies on Streptocarpus. III. Genetics and Chemistry of Flower Colour in the Garden forms, Species, and Hybrids. Heredity 11: 303-336.

Lawrence, W.J.C. 1957. Studies on Streptocarpus. IV. Genetics of Flower Colour Patterns. Heredity 11: 337-357.
4.  Dale Martens's hybridising notes
I borrowed this from the Streptocarpus Info forum pages.

Dale Martens's hybridising notes

Lesson 1

Selecting Parents

Decide what you would like to aim for:

1. Foliage

a. rosette

b. unifoliate

c. variegation

2. Blossoms

a. fantasy

b. yellow throat

c. double

d. scent

e. purple??

3. Size of plant

1.a.: Rosette shapes such as, Strep kentaniensis seem to be dominant. Streps ‘Gator’s Tail’ and ‘Lavender Rosette’ (Martens’ hybrids) are ‘Pegasus’ x S. kentaniensis are are rosette shaped. I understand from those using them as parents that the seedlings they’ve gotten are also rosette shaped, but not as strongly as that first generation.

1.b.: Unifoliate (single leaf) x Plurifoliate (multiple leaves) usually equals about 50/50 of each. Unifoliates are programmed to bloom, set seed, and die. One cannot propagate new plants from a unifoliate once it begins to flower. If you get a unifoliate seedling, do wait to see if it makes new leaves after it blooms. Often seedlings from unifoliate x plurifoliate initially produce one extra large and extra wide leaf. After the seedling blooms, then more leaves are usually produced, but they will never be as big as that first leaf. This is how ‘It Makes Scents’ and ‘Kiwi Friendship’ began their lives.

In addition, we’ve heard from Jaco Truter (and it’s my experience, too) that some (not all) plurifoliate seedlings with a unifoliate parent, tend to struggle to live after blooming. Although you are taking a risk when using a unifoliate parent, keep in mind that the unifoliate Strep dunnii with it’s crimson flowers is what is credited with giving us pink & reddish hybrids in the first place. I’m currently growing out hybrids with S. dunnii in the parentage and I have red flowers on some of the seedlings.

1.c.: Select a variegated plant as the Mother plant. So far crossing variegation x green leaf equals 99.9% green leaf seedlings. Those can be selfed or back-crossed to the variegated mother. If you are very lucky, and I’ve only been lucky three times, you can get a variegated seedling in that first batch of seedlings. Be sure to allow your seedlings to have time to sprout since some have suggested that they are slower to sprout than the average strep seedling. The only way we are going to get variegated plants with more than two flowers per stem is if we out-cross to green leaf plants that have lots of flowers. Caution: pretty please toss any variegated plants with weak flower stems. I saw a show that introduced some variegated streps and the flowers were practically laying on the leaves. Weak flower stems on variegated foliage is a real problem! Back-crossing will bring out those weak stems. I've gotten gorgeous variegated foliage by selfing the variegate x green leaf seedlings. About 8% had variegation.

2.a.: Fantasy flowers aren’t easy to obtain in hybridizing. Sometimes they have very little pollen. Sometimes the seedlings are very weak and die before reaching blooming stage. Fantasy x self has given me solid colored flowers. Fantasy x solid might give you fantasy. At this time I don’t know if the mother has to be the fantasy parent. Right now in my experience, it looks that way, but I haven’t hybridized them enough to say for sure. I have some ‘Double Scoop’ x ‘Toronto Silver Splash’ hybrids about to bloom.

2.b.: Yellow throats aren’t dominant. I used ‘Lemon Drop’ as the seed parent crossed with a strep without yellow in the throat and none of the seedlings had yellow throats. Even Texas Hot Chili x Big Yolk yielded a few seedlings with no yellow in the throat.

2.c.: Double flowers are dominant, but not to the extent we’d probably like. Double x single can yield some non-doubles, and the rest are either very double to having just a single, extra little petal. The male organs become extra petals. Therefore, a double must be the seed parent. Having said that, I found a double with one, distorted pollen sac stuck to a petal. I used that pollen on my double hybrid ‘Al’s Pal’. I got some flowers that were so filled with petals that the flower was unable to open! I also got some singles!! 'Double Scoop' is 'Al's Pal' x unnamed double.

2.d.: Scent appears to be a popular goal. So far those hybridizing for scent have used S. vandeleurii as a parent. It’s a unifoliate, so see 1.b. above. Jaco Truter has suggested that S. candidus be used. It’s a plurifoliate and the flower sure smells better than S. vandeleruii! One of the challenges with having a scented hybrid is that it has little or no pollen. Also, it seems to resist being hybridized. I recently discovered that scent from S. candidus can be passed onto the seedling through the pollen parent. One out of 10 plants has the scent, but it's quite mild and is more easily detected in the afternoon.

2.e.: Purple. Avoid it. Pretty please don’t name a purple flowered seedling unless it sings and dances. There are just too many purple/lavender/mauve streps in the world right now!

3. It seems like those of us in North America love the smaller streps. Those in England and Australia grow standard sized streps. Small x small doesn’t usually give you small plants. I’ve growing out Tim Tuttle’s Strep cyanandrus cross, ‘Cherokee Charm’ and it’s not small. I’ve also used small x standard and gotten standard sized plants. One needs to do a lot of back-crossing to get small plants with a variety of colors. It was suggested to me that Strep cyanandrus might not be a good parent to choose due to its intolerance of heat. We have some exciting hybridizing in the future if Strep liliputana will accept pollen from hybrids. I used its pollen on other hybrids, but they didn't accept it. Jaco has had some limited success with using it as a parent.

Lesson 2


When you are ready to cross your chosen plants:

1. The anthers, containing pollen, on the Father plant will mature first, producing viable pollen grain as soon as the buds open.

2. Initially the pistil (the female part in the center of the flower) is deep inside the flower. If you look closely, you will see the length of the pistil grow longer as days go by. The stigma (the very tip of the pistil which has a small opening) on the Mother plant will be most receptive 5 days after the bloom opens. On average the stigma stays receptive for 3 more days. I find it best to pollinate a flower right as the flower begins to look "old". That's about 10 days after opening.

3. Emasculating: Normally the pistil lengthens and eventually the receptive stigma may brush past the male organs, pushing open the anthers to self-pollinate. To prevent selfing the strep, you may want to remove the male parts. You’re going to laugh at this, but I want you to think of the male organs being similar in shape to a turkey’s wishbone. You know how two people pull apart the wishbone to make a wish? The part where the wishbone meets is where the pollen is and the two sides of the wishbone remind me of the filaments attached to the flower. You will see white filaments on either side of the Mother’s pistil. These filaments are attached to petals inside the flower. The pollen is at the tip enclosed in the anthers which are a darker color. If the two filaments are accidentally split apart (like a turkey’s wishbone), the pollen will disperse in the air and be wasted. Therefore, use a small pair of scissors and cut both filaments without splitting in half the anthers holding the pollen. Study the male organs. Why? You’ll need to be aware, once the anther is split apart, which side of the anthers have pollen.

4. Now that the male part is removed, cut off the petals on the flower to expose the pistil & stigma. This way you have clear access to fertilize the plant.

5. Ok, follow directions in #3, only with the Father plant. Carefully, without pulling apart the filaments, take the anthers to the Mother plant. Split the anthers open while touching them to the stigma. You will see the puff of fine pollen. Now you should have one half of the anthers in each hand. Rub the pollen side onto the stigma for added assurance that you’ll have a successful pollination. Repeat this procedure the next day using the same pollen parent on the same flower.

6. If you were successful, the rest of the flower should fall off within 24 hours. Within 2 weeks you will see the pod form and lengthen to at least 2 or more inches for the average hybrid.

7. Now you must tag the bloom. I purchase a plastic “string” of acrylic paints at a craft store. They have six or more little one-inch tubs of different colors attached to each other in a sort of plastic string for under $3, (especially at WalMart). I take a toothpick and dab a bit of paint on the back of one of the little green sepals on the calyx of the flower. That very same color is dabbed on a plastic tag. I write the date of pollination and the seed & pollen parents on that tag. Mother’s name goes first. This way I can pollinate as many flowers as I want and use a different paint color to represent different pollen parents. If you are pollinating two flowers at the same time with the same pollen parent, then use only one color representing that pollen parent.

You could also tie a strand of colored thread or acrylic yarn around the stem, instead of a label. Just write on the label red = ‘Joker’ or whatever pollen parent you used.

8. It can take from 8 to 12 weeks for the seedpod to mature. If it matures earlier, then the chances are that the seeds will not sprout.

10. When the seedpod is ready to be harvested, the stem of the seedpod will turn brown and begin to split. At this stage, cut the seedpod off and place on a sheet of paper (folded in half) to air-dry for 24 hours before sowing. The folded area catches the seeds. How many seeds in a pod? Zillions!!

11: A HUGE CAUTION: NEVER, EVER HYBRIDIZE A YOUNG STREP. It takes a lot of energy for streps to make seed pods. Wait until a young strep is flowering on its second leaf before using it as a seed parent.

Lesson 3

Sowing Seed

1. Find a smallish, clear plastic container with a clear lid. Put about 1/2 an inch of moist, not soaking wet vermiculite/perlite in the bottom and then on top of that put a half inch to one inch of moist, not soaking wet, AV soil or peat from a peat pellet. Use only distilled water or tap water to moisten the soil. Don't use fertilized water. Tamp the soil down so that it is level and air pockets have been dislodged. You’ll need a minimum of 1-1/2 inches from the top of the soil to the container’s lid for the seedlings. Remember the label you made when you first crossed the mother plant? Add the date you sowed the seeds and put that in the container. If the container is large enough for more than one batch of seeds, then have the writing face the seeds sown. I frequently have 5 or more seed batches growing in one container.

2. Take a five inch or so white piece of paper and crease it down the center. This is to make it easier for you, when sowing your seed.

3. Your seedpod should be brown and partially split at this stage. Slit it open further, over the piece of creased, white paper. Make sure you scratch all the seeds out of the seedpod. I use a sewing needle or toothpick.

4. Gently pick up the white paper and hold it at an angle, so you will be able to distribute the seed evenly into your prepared seed container.

5. It is advisable not to sow all your seed at once for a couple of reasons. One is that something awful might happen to the seedlings (drought, algae) and the other is that there’s going to be a zillion seeds! Store the rest of the seed in the refrigerator. I prefer to sow enough seed for about 30 plants.

6. Tap the side of the paper holding the seed over the moist soil and try to scatter the seeds. If you tap gently, you will find that just a few seeds will go down to the edge of the paper and you can place them more or less where you want.

7. Snap the clear lid on to the container.

8. Place the seed box under your lights about 6 inches to 10 inches below the tubes.

9. If you are growing under natural light only, make sure that no direct sunlight falls on the seed container which will bake your seeds. Also when growing under natural light, the reservoir will form green algae much more quickly.

11. The seeds will start to germinate within 12 - 30 days, some might take longer, so do not be in a hurry to dispose of the seed container. Just leave it where it is and be patient a while longer. Seed from species can take a couple of months to sprout. Variegated seedlings may take about 30 days to sprout, so don’t be disappointed too much if you don’t see variegation right away on the seedlings that have a variegated parent. Do check the container for moisture, since you don’t want it to dry out while you’re waiting to see sprouts. Add only distilled or tap water, don't add fertilized water.

12. Don't forget to take notes as to what date you sowed the seed and how long they took to germinate. It’s easier if you add the date of sprouting to that label that gives the parentage. All of your information is on that label. As soon as the seedlings are transplanted, you might transfer the information to a 3 x 5 index card.

Lesson 4


1. I prefer to transplant seedlings often. One can get a blooming plant from a sprouting strep seed in 4-1/2 months if the strep seedling is transplanted often to stimulate growth.

2. Use an AV “baby mix” of 50% AV mix and 50% vermiculite. Make sure it’s moist, not soaking wet. Use a similar container like you did for sowing seed. You’ll need a lid for the container.

3. When the seedlings are 7 days old, use a wooden toothpick to lift the seedlings. Gently pull each seedling apart from its neighbors. If there’s a grouping of seedlings that seem all stuck together, then put that group in a shallow dish of water and use two toothpicks to swish the water and to help separate them. Even if the roots come off, plant the seedling anyway. You may plant the seedlings about 1/4 inch apart. That’s plenty of room for each to grow for the next two weeks.

4. If you have sown variegated seed or species seed, be sure to keep the original container after you have removed all visible seedlings, and make sure it doesn’t dry out. Check it once a week to look for new sprouts.

5. Two weeks after that first transplanting, take a 2-1/2 inch square pot and put wicks on each. Use the “baby mix” again. Then put 9 seedlings in that pot, 3 rows, 3 across. No need this time for a lid or 100% humidity. Just make sure your wicks are working. It’s easier for me to put lots of square pots in one of those rectangular, black trays and water them as a group rather than on individual reservoirs. Use a balanced fertilizer at the rate of 1/8 teaspoon per gallon of water.

6. Two weeks later, lift up each seedling and plop it down in that same pot. That’s all!

7. After another two weeks, now it’s a judgement call as to how many seedlings remain in that 2-1/2 inch pot. You should have at least 2 or 3. Caution: don’t ever bury a strep seedling (or mature plant!) lower in the pot than it was previously grown. It’s not an African violet! Be careful about this, please.

8. Another 2 weeks has gone by. This time perhaps each seedling gets its own 2-1/2 inch pot. I never give a seedling a larger pot than that until it blooms and proves it is worth keeping. At this time you may use whatever mix you prefer to use for an adult strep.

9. All white, or almost all white seedlings rarely live. You can try high nitrogen fertilizer at the rate of 1/8 teaspoon per gallon of water, but I’ve not found that to be very successful.

June 2005
4.  Gesneriaceae - A Scientific Perspective
     "Gesneriaceae - A Scientific Perspective" is a great article on the Gesneriad Reference Web, with portions about Streptocarpus, in various sections.
Anderson's Streptocarpus,
11 Oct 2011, 21:37
Anderson's Streptocarpus,
11 Oct 2011, 21:37