INFLORESCENCE MORPHOLOGY (Inflorescence: Is a.k.a. the infructescence when the flowers have set fruit) Definition: Inflorescence is the reproductive shoot system (a shoot system bearing flowers) But note: Often the boundary between the vegetative and reproductive parts of the plant is a bit fuzzy! Classification of inflorescences: There is no completely satisfactory system, but the following descriptive/ morphological system is used extensively: Inflorescences are defined based on. (1) The overall shape and branching pattern (2) Whether the shoot growth along the main axis (the rachis) is predominantly sympodial (= cyme-based inflorescences) or monopodial (= raceme-based inflorescences) SYMPODIAL (lateral branches take over) MONOPODIAL (Same shoot apex all along the main axis) (3) Whether growth on the main axis stops (= determinate growth: all cymes) or can continue indefinitely (= indeterminate growth: many but not all racemes) (4) Whether the inflorescence is simple or compound (if compound, the repeated units are called paracladium; Fractal-like morphology where a given shape is repeated at different levels of organization) 1
Overall definitions: Cyme-based inflorescences: (i) Sympodial growth (ii) Growth along the inflorescence axis is determinate, (iii) Can usually recognize them by noting that The flowering sequence begins with the terminal (top or central) flower in an inflorescence and its subunits Raceme-based inflorescences (i) Monopodial growth (ii) Growth along the inflorescence axis can be determinate or indeterminate (iii) Can usually recognize them by noting that The flowering sequence begins at the base (or outside) of the inflorescence and its subunits Major types of inflorescence: (1) Solitary flowers! 2
(2) Raceme-based inflorescences Remember: The main axis of a raceme is monopodial, and the flowering sequence starts at the base of the inflorescence RACEME CORYMB SPIKE PANICLE SPADIX Notice whether each flower has a pedicel, or is sessile (. spikes!) Also, The panicle is just a compound raceme The corymb is just a raceme where the entire inflorescence is flat-topped The spadix is just a spike with a swollen main axis! 3
(3) Cyme-based inflorescences Remember: The main axis of a cyme is sympodial, and the flowering sequence starts at the terminal end of the inflorescence SIMPLE CYME COMPOUND CYME HELICOID CYME SCORPOID CYME 4
(4) Some inflorescences are easy to recognise by shape but it may not be immediately obvious if they are fundamentally cymes or racemes or a mixture of the two!) UMBELS CAPITULUM CATKIN FASCICLE THYRSE Some other things to note about inflorescences One (or two) bracts (= reduced leaves) are found below the entire inflorescence, and below each flower, BUT these have been lost to varying degrees in different groups of flowering plants Many of the simple types of inflorescence described above can be units within compound infloresences (eg, umbels of umbels) 5
FRUIT TERMINOLOGY Refs: Harris & Harris pp. 184-188, Judd &co pp. 66-68 Quite a lot of variation in how botanists define fruit types! The system is not completely logical but has become well embedded in the descriptive literature. Definition of a fruit: Structure bearing or containing the seeds (= fertilized ovules) regardless of its edible qualities! A fruit is a mature, ripened ovary (containing the seeds), together with any adjacent parts fused at maturity We need to have a good idea of the types of fruit listed below. (A) Fruits formed from more than one flower: MULTIPLE FRUIT: derived from an entire inflorescence (eg pineapple) (B) Fruits formed from one flower but more than one ovary ( carpels are apocarpous): AGGREGATE FRUIT: Separate (apocarpous) carpels from one flower that become aggregated at maturity (eg raspberry, blackberry) ACCESSORY FRUIT: Separate (apocarpous) carpels are borne on the surface of a fleshy receptacle. Ripened ovaries are small achenes (see below) dotted on the surface of the receptacle (eg strawberry) 6
(C) Fruit formed from one flower and ovary. Remember: The ovary may constitute a single carpel or multiple fused (syncarpous) carpels The major types of fruit are defined based on whether: The fruit wall (pericarp) is at least partly fleshy at maturity, or if it is dry If the fruit wall is dry, whether it is dehiscent (= splits to release seeds) or indehiscent Some other features, such as how many carpels and whether winged or not (1) Fruit fleshy at maturity and indehiscent (not releasing seeds) BERRY: Ovary wall (pericarp) is entirely fleshy 1 or more carpels (eg tomato, blueberry) DRUPE: Pericarp is fleshy apart from a stony, woody endocarp that is tightly attached to the seed in a single carpel (eg peach, plum, cherry) POME: Found in Rosaceae. The fleshy part is derived from perianth (and perhaps receptacle) tissue, rather than ovary tissue. The actual ovary wall (pericarp) is papery and thin in the centre of the fruit (eg Apple, pear, quince) 7
(2) Fruit is dry at maturity and indehiscent (= not releasing seeds) Fruit of a single carpel -- ACHENE: Small and 1-seeded, the fruit wall close-fitting and not particularly hard and tough (eg strawberry achene, sunflower) SAMARA: Winged achene (eg elm, ash, tulip tree) UTRICLE: 1-seeded; fruit wall is thin-walled and more or less bladdery-inflated, the seed is relatively loose from the wall Fruit of more than one carpel NUT: Bony outer wall, 1-seeded (but by abortion!) (eg oak, hazelnut) SCHIZOCARP: The mature indehiscent fruit splits into 1-carpellate segments, each containing single seeds (eg carrots, maple) 8
(3) Fruit is dry at maturity and dehiscent (meaning it sheds seeds) Fruit of a single carpel FOLLICLE: Fruit splits along one side (eg columbine, milkweed) LEGUME: Fruit splits along both sides (eg Fabaceae) A LOMENT is a legume with constriction between the seeds (these break into segments) Fruit of more than one carpel SILIQUE: 2 carpels, opens along two valves, leaving a septum (eg Brassicaceae) A SILICLE is a type of silique that is less than twice as long as wide CAPSULE: Multiple carpels with seeds released in various ways: PORIDICAL CAPSULE: releases seeds through pores (eg poppy) CIRCUMCISSILE CAPSULE (or PYXIS): A capsule with a lid! LOCULICIDAL CAPSULE: releases seeds by splitting along outside centre of each locule (eg Iris, Viola) SEPTICIDAL CAPSULE: releases seeds by splitting along the septae between locules (carpels) (eg Rhododendron) 9
Fruits can also be defined by their mode of dispersal, eg: Wind-borne (winged, dandelion-like, or explosive) Water-borne (ocean-dispersed, rain-shed) Animal-borne (attractive and fleshy, inconspicuous and hooked or sticky) 10