Adaxial (and abaxial)

When referring to a structure such as a leaf or flower, adaxial refers to the part that "faces" the stem (axis).  In this nomenclature, the leaf or flowerstalk is thought of as being above the horizontal (whether it actually is or not), so the adaxial surface of a leaf is the upper side.

It may help to recall that the adaxial side of the leaf is the same as the one adjacent to the axil.

The opposite of adaxial is abaxial.  (Latin prefixes ad- [toward] and ab- [away from].)

When referring to flower parts, adaxial is synonymous with dorsal, which is the more frequently used term, especially in reference to nectaries.


When referring to leaves, alternate means one per node.  The opposite of alternate is, um, opposite.

When referring to multiple structures and used as a verb, "alternate with" means to occur in the intervals between some other structure.  For an example, see the discussion of nectaries and how they alternate with the calyx lobes (in e.g., Sinningia gerdtiana).


Floral anatomy

A stamen, the male part of a flower, is ordinarily composed of a stalk, called the filament, and a pollen dispenser, called the anther.  In the Sinningieae, there are four stamens, with their filaments anchored at their bases to the corolla tube.  The filaments are epipetalous, meaning that each filament base is attached to the tube at the center of what would be a petal if they weren't joined into a tube, but is therefore halfway between the notches marking the boundary between the corolla lobes.  Since there are five lobes and only four stamens, there must be one lobe which does not have a stamen, and it is naturally the one which does not have a symmetry partner, namely the bottom (abaxial) lobe.

In the Sinningieae, even though there are four separate filaments, the four anthers are joined into a rectangle, which presents the pollen to the prospective pollinator in a well-defined posture.

In peloric sinningia flowers, such as those of some S. speciosa varieties, all the corolla lobes are the same, with the result that each has a stamen, meaning that there are more than four anthers combined.  The picture of Sinningia speciosa does not show it very well, but that flower has six stamens, and therefore six anthers.

Axil (adjective form: axillary)

The axil is the notch between a leafstalk (petiole) and the stem.  The axil normally contains a dormant bud which could develop into a stem or a flowerstalk under appropriate conditions.  The most usual circumstance which would cause the development of a stem is the removal by accident or intention ("pinching") of the growing tip of the main stem.  A growing tip (meristem) very often releases significant amounts of a growth inhibitor which prevents the development of secondary shoots in the axils of its stem.  When the meristem is removed, the inhibition is removed too, so one or more secondary shoots may develop.

Flowerstalks normally develop in axils, as can be seen from the photograph of Sinningia sp. "Black Hill".

Etymology: from Latin axilla "armpit", from same root as "axis".


A bract is a leaf, usually small, which (usually) bears in its axil a pedicel or peduncle. As such, it is a part of a flowering axis.

For an example of bracts, see here.


Bell-shaped, from Latin campana.  In gesneriads, campanulate flowers are often called "slipper" flowers.

Sinningia speciosa has campanulate flowers.  The peloric flowers are the extreme form of campanulate-ness (campanulicity?).  Others with campanulate flowers are Paliavana prasinata, S. eumorpha, S. conspicua, and S. richii.


Think of a leaf with seeds attached along its margins.  This is believed to be the evolutionary origin of the carpel, the structural subunit of the ovary and of the fruit that an ovary develops into if its ovules have been fertilized.  Another page has a more detailed discussion.


A flowering-plant seed contains one or two embryo leaves.  These leaves are called cotyledons.  In a few families (such as legumes and grasses), the embryo leaves remain underground when the seeds germinate, but mostly they appear above the ground as the plant's first photosynthetic leaves.

The flowering plants are subdivided by the number of cotyledons.  Dicots, constituting about 4/5 of all flowering-plant species, have two cotyledons, while monocots have one cotyledon.

Gesneriads are dicots.  For most plant families, that's the end of the story.  Number of cotyledons = where the family belongs.  Nothing more of interest about cotyledons.

But for gesneriads, the cotyledons have more to tell.  The cotyledons behave quite differently in the two halves of the Gesneriaceae.

In the western-hemisphere branch, the cotyledons are normal and boring.  Two of them, same size, expand, and eventually fall off.  Just like, say, impatiens.

But in the eastern-hemisphere branch, the cotyledons are not normal and boring.  One of them grows, the other remains stunted.  Sometimes a gap opens between them on the stem, so that the expanded leaf is higher up the stem than the other one.  Soon, the small leaf falls off.

In most species, the expanded (or accrescent) cotyledon eventually suffers the same fate as the normal cotyledon: it withers and falls off.  But in some species, such as the unifoliate streptocarpus, that cotyledon is all the leaf the plant ever gets.  There is no real stem, no other nodes, no other axils.

It isn't just Streptocarpus which has managed this trick either.  Certain other genera, such as Monophyllaea, also retain the accrescent cotyledon, and may not ever have another leaf.  This unifoliate habit is clearly a trick which depends on that original cotyledon on steroids.  No body-builder cotyledon, no single-leaf plant.  This gesneriad innovation in the use of plant parts does not apply to the western-hemisphere branch, including the Sinningieae, which all have normal plant development.  Or do they?

Sinningia defoliata and Sinningia helioana certainly don't look like they have normal plant development.  Probably, the peculiar habit of these plants is due to specializations based on having tuber, not on some inclination toward leaf-development weirdness expressed more openly and completely in the other half of the family.  There is no reason to believe the cotyledon strangeness originated before the split between the two halves of the family.

Pay no attention to the man behind the screen...


The decussate leaf growth pattern is a special case of opposite leaves.  Traversing the stem upward, each leaf pair is at right angles to the leaf pair just below it.  This means that a given pair of leaves is on top of the leaf pair two nodes down, since both are at right angles to the leaf pair between them.

It's not clear what the advantage of this arrangement is, since it means that leaves will be shaded by those above them, but the decussate pattern is not uncommon in plants, including Sinningia richii and Sinningia macrophylla.

The preferred pronunciation is supposed to be deCUSSate, but DECussate is also given.  The word isn't DE + CUSS + ATE, but rather derived from Latin decem, meaning "ten" (as in "December"); the origin of the word refers to the X pattern created by the leaves, X being the Roman numeral for 10.

The decussate pattern is one kind of phyllotaxis.

Dehisce, Dehiscent

Dehisce is a botany term for "split open", as a fruit.  A dehiscent fruit is one which splits open, like a sinningia capsule.  Indehiscent fruits are those which do not split open, like columnea berries.

In general, dry fruits dehisce, because they rely on wind to disperse the seeds.  In general, moist or juicy fruits do not dehisce, because they rely on an animal to eat the fruit and disperse the seeds.  This is certainly the case with columnea (juicy) and sinningia (dry) fruits.

There are plenty of exceptions to both generalities.  Within the Gesneriaceae, the genus Nematanthus is characterized by (roughly speaking) dehiscent berries.  The berry-like fruits split open at maturity to display a brightly-colored interior laden with seeds.  An animal (perhaps an ant) comes to the fruit for the food and carries away the seeds.

Dry indehiscent fruits are common too. Walnuts, sunflowers, and peanuts are good examples, all from widely separated families.

The word dehisce is derived from a Latin root meaning "gape".  The same root gives us the word hiatus.  The Latin root is ultimately derived from the Indo-European root ghai, which is also the linguistic ancestor of words like yawn and chasm.


Determinate, in reference to plant growth patterns, means that the plant has a predetermined number of leaves or stem nodes, and then produces zero or more inflorescences.  A blooming-size Sinningia leucotricha is determinate, while its juvenile form is indeterminate.


Dicotyledons, or dicots for short, are flowering plants which have two seed leaves (cotyledons).  About 80% of flowering-plant species are dicots; the remainder (monocots) include grasses, orchids, bromeliads, palms, lilies, and aroids.  See monocots.


Think Jaws.  The dorsal fin is the one that sticks out of the water and causes pounding theme noise to start.

"Dorsal" means (pertaining to) the back.  Years ago, when I was having trouble remembering the difference between dorsal and its opposite (ventral), my mnemonic was that Tony Dorsett was a running back in American football.  Fortunately, I no longer need the mnemonic, given that Mr. Dorsett has long since retired.

When applied to sharks, back refers to the upper side of the body.  When applied to leaves, back refers to the underside.  Not so helpful, huh?

Perhaps because of this ambiguity, dorsal and ventral are not often used in reference to leaves.  Instead, the terms adaxial and abaxial are preferred.

Where dorsal is used is in reference to nectaries in a flower.  If you are looking at a flower face on, with the pistil (style/stigma) pointing directly at your nose, the dorsal surface is up, just as it is in a shark.

I don't know whether dorsal is used in the case of resupinate flowers, where up/down and back/front get a little mixed up.


Most plants grow in the ground, with their roots in the dirt.  These plants are called terrestrial.  A few plants grow in trees, almost always in tropical or semi-tropical rain forests.  Their roots anchor in leaf litter which has collected in favorable locations in a tree: notches between tree branches and tree trunks, depressions in the branches, or clusters of twig bases.

Families which contain a large number of epiphytes include the Orchidaceae and Bromeliaceae.  In the cactus family, two subgroups (rhipsalids and epiphyllids) are almost entirely epiphytes.

In the Gesneriaceae, Nematanthus and Columnea are among the genera which have explored the epiphytic opportunities.  In the Sinningia tribe, there are only two epiphytic species: S. cooperi and S. douglasii.


This is a verb meaning to become white through loss of normal color.  Plants growing in heavier shade than they are adapted to often become etiolated.

Such stems often elongate abnormally, as the plant tries to find sufficient light to grow.  Whiteness and elongation are often found together when light is too low, so the elongation is sometimes called (inaccurately but understandably) etiolation.


ex- means "out", so this ought to be the opposite of inserted.  Not quite, but close.  When applied to anthers, exserted means that the anthers project beyond the flower (corolla tube), as in Sinningia sellovii or Sinningia amambayansis.

Flowers with a galea usually have their anthers exserted beyond the corolla tube proper but still underneath the galea.


Happening only in response to certain circumstances, or the absence of certain circumstances, or as one option among other possibilities.  Sinningia douglasii is a facultative epiphyte, meaning it can grow nonepiphytically too.  Some sinningias have stems which are facultatively deciduous, meaning that they will drop off the tuber if the weather is cold or dry enough, but are retained if conditions are favorable.  The opposite is obligate.

One way of thinking about it is that facultative properties are determined by a combination of heredity and environment, while obligate properties are determined entirely by heredity.


Imbricate, in reference to the parts of a calyx or corolla, means overlapping.  The best example is the rolled-up bud of a hibiscus flower.  The opposite of imbricate is valvate.


Indeterminate, in reference to plant growth patterns, means that the plant does not have a predetermined number of leaves or stem nodes.  It may flower in the axils of an extended axis or normal leaves.  A plant with indeterminate growth can have as many flowers as its growing conditions permit, while the number of flowers on a plant with determinate growth, while not completely circumscribed, is not as flexible.  The juvenile forms of some sinningias have indeterminate growth while their flowering forms have determinate growth.


This term is used for two related concepts:

  1. The segment of a stem between two adjacent nodes
  2. The length of the segment defined in part #1

Thus the internodes of some sinningia species are hairy, while the internodes of many plants will increase if the plants are grown in insufficient light (this is called etiolation).


Suppose there is a five-room house, but the owners are dissatisfied with the arrangement and decide to remove some of the interior partitions.  The house may still show some structural evidence of its original five-room design, but after the partitions have been removed, there will only be (let us say) two rooms.

The five original rooms are analogous to the carpels of an ovary or fruit.  The carpels are the structural subunits of the house.  The two post-remodeling rooms are analogous to the locules of an ovary or fruit.  The carpels show how many subunits went into the development of the ovary, while locules represent the actual outcome.

Gesneriads and their relatives are descended from "five-room" ancestors.  The original gesneriad fruit probably had two "rooms", but the partition between them has been partially or entirely removed.  In sinningia fruits, the placentas are the only visible remnant of the structural division between the carpels.

Another page has more discussion.


When cells divide, normally each of the two daughter cells receives a full set of the cell's chromosomes.  As part of the cell's preparations for division, each chromosome makes a copy of itself -- one chromosome goes to one daughter cell and the copy goes to the other daughter cell.

This is the "normal" type of cell division, responsible for growth and the creation of new organs, such as leaves and flowers.  It is called mitosis.

However, in the division of reproductive cells, involved in the creation of pollen grains, ovules, and (in people) sperm and egg cells, a more complicated process takes place resulting in only one set of chromosomes in each daughter cell.  This is called meiosis.

For example, mitosis in sinningia cells results in new cells possessing a full complement of 26 chromosomes, while meiosis yields daughter cells containing 13 chromosomes.


A point where plant growth takes place.

The meristem consists of undifferentiated cells, which can generate the various types of tissue needed by the plant.  In this they resemble the stem cells in animals, but meristems can persist for the life of a plant.  The apical meristem is the one at the end of a shoot, where new stem, leaf, and floral tissue is created.  The cambium or secondary meristem in dicots is where supporting tissue for the stem gets expanded.  A branched inflorescence such as the gesneriad cyme can have multiple meristems working at any given time.


This is not bad breath.

When cells divide, normally each of the two daughter cells receives a full set of the cell's chromosomes.  As part of the cell's preparations for division, each chromosome makes a copy of itself -- one chromosome goes to one daughter cell and the copy goes to the other daughter cell.  This version of cell division, in which each daughter cell is (supposed to be) identical to the parent cell, is called mitosis.

This is the "normal" type of cell division, responsible for growth and the creation of new organs, such as leaves and flowers.

The other type of cell division, responsible for reproduction, is called meiosis.


Monocotyledons, or monocots for short, are flowering plants which have one seed leaf (cotyledon).  About 20% of flowering-plant species are monocots.  They are distinguished from the remainder (dicots) by:


This is the point on a stem from which a leaf emerges.  In most gesneriads (including sinningias), there will normally be two leaves per node.  The active region between the stem and the leaf is the axil, and it is from this axil that new branches and flower(stalk)s emerge.

Nodes don't necessarily have to have attached leaves.  The leaves may have fallen (have undergone abscission) or be modified to the point of unrecognizability (as in cactus spines).

The segment or distance between two nodes is called the internode.


Determined entirely by an organism's genetic properties, and not by circumstances.  Most sinningias are obligate tuber-formers; they will make a tuber regardless of the circumstances they are growing in.  Sinningia douglasii is obligately deciduous; the leaves and stem drop from the tuber when winter arrives, regardless of how warm and moist it is (assuming that the plant is not prevented from discovering that winter has arrived).  The opposite of obligate is facultative.


When referring to leaves, opposite means two per node.  The opposite of opposite is alternate.


This part of the flower encloses the ovules, which will develop into seeds if they are fertilized by pollen.

The best place to see an ovary is behind a daffodil flower or a female cucumber flower.  These ovaries look like miniatures of the fruits they will become if they are fertilized.


A pedicel is the stalk of an individual flower.  It may arise singly from the stem (as in Sinningia conspicua, most of the time) or it may arise from a compound flowerstalk called a peduncle.


A petiole is a leafstalk.  It connects the leaf blade to the stem.


Flipped over on its back, usually applied to flowers, but it can be applied to any structure (such as a leaf) which has a well-defined top and bottom.

See a discussion.

Sister species or sister group

Suppose we have a relationship tree that looks like the diagram below, where the subdivisions and internal structure of Groups A and B are ignored.


               _____________ Group A
              |_____________ Group B

We then say that Group A and Group B are sister groups, regardless of their internal structure.  The crucial criterion is that A, B, and A+B are all clades.

For a real example, the Corytholoma clade tree, slightly simplified, looks like this:

                              __C__ corytholoma core group
                       |     |
                       |     |__D__ S. barbata
              |        |
              |        |__E________ S. aghensis and the miniatures
              |___F________________ S. richii

Here, branch F is sister to branch A (and vice versa), branch E is sister to branch B (and vice versa), and branch D is sister to branch C (and vice versa).  The fact that branch F and branch D comprise just one species each while branch E is made up of several species is irrelevant, since the internal structure of a sister group does not enter into the definition.

If the sister group does consist of a single species, then it is called a sister species.  Thus, S. richii is a sister species to the rest of the clade, and S. barbata is a sister species to the corytholoma core group.


A leaf or flower is called sessile if it originates (to the naked eye, anyway) directly from the stem without its own stalk (petiole).


The style is the stalk for the female part of the flower.  At the outer end of the style is the stigma, which is the receptive area upon which pollen is deposited.  The pollen grains germinate, grow down the style to the ovary, where they fertilize ovules, which develop into seeds.  If everything goes right.


A taxon (plural: taxa) is a taxonomical category.  In the plant kingdom, the major taxa are species, genus, family, order, and class.  Other taxa can be defined by adding sub- or super- to a given taxon name, e.g. superfamily or subspecies.  There are other taxa which are not derived from the major taxa, such as tribe (above genus and below subfamily) and variety (below subspecies).

The word taxon is convenient when one wishes to refer to a group of organisms without getting involved in an argument about taxonomy.


DNA-based organisms have their genes (and the DNA which makes them up) organized into chromosomes, like a long string of beads.  Sexually reproducing plants and animals have chromosomes in pairs.  One chromosome of each pair is inherited from each parent, and one chromosome per pair is imparted to an offspring.

Hybrid plants descended from two different species will receive slightly mismatched chromosomes, with many of the same genes but some differences.  In certain cases, these differences are not enough to prevent the organism from growing normally, but are enough to prevent reproduction.  For example, a hybrid plant will be sterile if the reproductive cell divisions (called meiosis) essential for creating pollen grains and ovules cannot work properly due to chromosome incompatibilities.

This is normally a dead end, but sometimes an accident in the creation of the hybrid plant results in it having a full set of chromosomes from each parent.  For example, a sinningia normally had 26 chromosomes: two sets of 13 chromosomes each.  One set of 13 comes from the pollen parent, the other set from the seed parent.  In the accidental case, however, a sinningia will wind up with 52 chromosomes, 26 from each parent.

The normal sinningia, with two sets of 13 chromosomes, is diploid.  The normal human being, with two sets of 23 chromosomes, is also diploid.  The normal sinningia pollen grain and the normal sinningia ovule, with only one set of 13 chromosomes, is haploid, as are human sperm and egg cells (and just for jollies, so are the males of ants, bees, and wasps).

The fluke sinningia, with two sets of two sets of 13 chromosomes (and thus 52 altogether) is called tetraploid.  Even in a hybrid with mismatched parents, a tetraploid plant will always be able to pair up its chromosomes for meiosis.  Thus it will not be sterile.

This is not just an abstract issue, or something relegated to the gesneriad suburbs of biology.  Human civilization took off with the invention of agriculture, and the key event in the development of agriculture was the domestication of wheat.

Cultivated wheat is a hexaploid, with three sets of paired chromosomes.  Most of the calories that humans consume come directly or indirectly from grass-family plants, and those plants include the robust and productive hexaploid wheat (genus Triticum) as well as cereal plants (such as oats and rye) which "domesticated themselves" as weeds in cultivated wheat.

Tetraploidy can restore fertility to sterile plants, but it is almost never a good thing for animals, because their bodies are more tightly integrated than those of plants, and therefore much more sensitive to imbalances.  Twice as much of everything will result in something very bad for an animal that must move around in a coordinated manner.

[You would think that half as much of everything wouldn't work either, but somehow those haploid bee males (aka drones) manage to fly, one of the most complex and highly coordinated operations of any animal.]

Type species

The original description of a genus is supposed to be linked to a type species.  The genus and species are henceforth inextricably linked.  Whither the genus goeth, so goeth the type species.  Whither the type species goeth, so goeth the genus.

Thus, if the genus Sinningia were broken up into several genera, the piece that contained Sinningia's type species, S. helleri, would be the one to keep the name Sinningia.  All the other constructed or revived genera would have to receive other names.

The type species for Rechsteineria was R. allagophylla, now S. allagophylla (thank you to Christian Feuillet for that information!).  Thus if Rechsteineria were revived, it would have to include R./S. allagophylla.

The type species for Vanhouttea is V. calcarata.

The type species for Paliavana is, at least according to the Weber/Skog Gesneriad Genera web site, unspecified.


Valvate, in reference to the parts of a calyx or corolla, means in contact but not overlapping.  A good gesneriad example is the calyx of a Paliavana tenuiflora flowerbud.  The opposite of valvate is imbricate.


Even though this word is pronounced "zero fight", it does not mean "dead wimp".  The two roots are xeros, Greek for "dry", and phytos, Greek for "plant".  It refers to a drought-tolerant plant.

In regions where water shortage is a present or impending reality, growing xerophytes is a good adjustment.  Xerophytes include not only obvious succulents such as the cactus family and the iceplants (Aizoaceae), but also drought-adapted herbaceous plants of western North America, such as penstemons.