Plant Taxonomy - Biology 308

Plant Taxonomy (BIOL308) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe/

Floral Formulas

A floral formula is a convenient way to store and retrieve information about plants. There is no one correct method for writing a floral formula. We will use a version that is modified from one of my graduate school mentors at the University of Illinois, Dr. David A. Young. This version is similar to that of Hickey and King (1999).

The basic floral formula summarizes the following features (in order):

Floral Symmetry
Is the flower actinomorphic (symbolized by an asterisk, *) or zygomorphic (z)?
Sex/breeding system.
The sexuality of the flower is represented by the standard symbols for males (♂) and females (♀). Thus a species with imperfect flowers plant would be symbolized (♂ ♀) and a perfect flower is symbolized by (c = combined symbol, can't figure out how to draw it yet) which represents the merger of the symbols for a male and a female. If the flower is imperfect the breeding system can be specified by using an "M" for a monoecious system and "D" when dioecious. Other abbreviations include polygamomonoecious (PM) and polygamodioecious (PD).
Calyx.
Symbolized by the letter "K". The number of sepals in the calyx is give following the K. The degree of fusion of the sepals can be indicated by circling the sepal number. Thus, a flower with five separate sepals would be symbolized K 5. A flower with five basally connate sepals would be K 5. If the five is completely circled, then the sepals are completely fused.
Corolla.
Symbolized by the letter "C". The number of petals and degree of fusion is represented as above. The symmetry of the corolla is assumed to be regular (actinomorphic). If irregular (zygomorphic), this is represented by a "z". As an example, an irregular corolla of five basally-connate petals would be symbolized: Cz 5.

Androecium.
Symbolized by the letter "A". The number of stamens and degree of fusion can be represented as described for the calyx. In addition, if the stamens are epipetalous, a line can be drawn connecting the K and A. For example, a petunia has five epipetalous stamens. This would be represented C 5; A 5.
Gynoecium.
Symbolized by the letter "G". The number of carpels and degree of carpellary fusion is expressed in a similar fashion to sepals. The ovary insertion (inferior, superior) can be represented by a line drawn above or below the "G". For example, a unicarpellate gynoecious with a superior ovary would be symbolized G 1. An apocarpous gynoecious comprised of 3 separate carpels and a superior ovary would be represented G 3. A syncarpous gynoecious comprised of four carpels with an inferior ovary would be G 4 (imagine a short line above the G and the 4 in a circle – I’m still trying to figure out how to do that on the computer. If it is highlighted in yellow imagine a circle around the numbers).
Fruit Type.
The floral formula includes an abbreviation for the type of fruit (for example, ach. = achene, b. = berry, cap. = capsule, dr. = drupe, hesp. = hesperidium, sam. = samara, foll. = follicle).
Miscellaneous.
Any unique information about the plant can be included at the end. For example, it may have a milky sap, or stinging hairs, or be a vine. If the condition occurs sometimes it is put in parentheses

Summary:
The features listed above are written out separated by a semicolon. If the feature is sometimes present it is included in parentheses. Numerous parts are indicated with the infinity symbol. Here are a few examples.

Floral Formula #1: *; c (♂ ♀, D); K 5; C 5 (0); A 5-10 (5-10); G 2-5 ; cap., (ach)

Interpretation: Fls. actinomorphic; bisexual (rarely unisexual and then the plants dioecious); calyx of 5 basally connate sepals, corolla of 5 distinct petals (or rarely apetalous), stamens 5-10 and distinct (or rarely 5-10 and basally connate), gynoecium syncarpous with 2-5 carpels (imagine a circle around the 2-5), ovary superior; fruit a capsule (or rarely an achene).

Floral Formula #2:

*; ♂ ♀, M ♂ fls.: K 3-6; C 3-6 (3-6); A 3-5; G 0
♀ fls.: K 3-6; C O, G 5-9; ach

Interpretation: Fls. actinomorphic; unisexual and the plants monoecious; staminate fls. with a calyx of 3-6 basally connate sepals, corolla of 3-6 free or sometimes connate petals, stamens 3-5 and distinct; pistillate fls. with a calyx of 3-6 basally connate or free sepals (imagine a dotted line under the 3-6), corolla absent (=apetalous), gynoecium apocarpous with 5-9 carpels, ovary superior; fruit an achene.

Floral Formula #3:
♂ ♀, M (D) ♂ fls.: P 0; A 1; G 0
♀ fls.: P 0; A 0; G 3; samara-like nut

Interpretation: Fls. unisexual and the plants typically monoecious or sometimes dioecious; staminate fls. without a perianth (naked) and with a single stamen; pistillate fls. naked, gynoecium syncarpous with three carpels (imagine a circle around the 3), ovary superior; fruit a winged samara-like nut.

Floral Formula #4: z; c; K 5, 5; C 5; A 5 (5); G 2; 2 foll

Interpretation: Fls. zygomorphic; bisexual; calyx of 5 free or basally connate sepals; corolla of 5 connate petals, stamens 5 and distinct or sometimes connate, gynoecium apocarpous with 2 carpels that are apically fused (imagine a line over the 2), ovary superior; androecium adnate to gynoecium (imagine a line drawn over the A and G); fruit of 2 follicles.