Purple flower air dispersal seed weed
Reference: Harper (1977), Ch. 2, The seed rain, pp. 33-60; summary p. XIV
Reference: Agronomy 517 class discussions 1991-2002
1: outward spreading of organisms or propagules from their point of origin or release; one-way movement of organisms from one home site to another
2: the outward extension of a species’ range, typically by a chance event; accidental migration
Dispersal affect on population size at a locality
-Population size: habitable sites and dispersibility
– Dispersal mechanisms of a plant species seed indicate how it seeks habitable sites over a patchy landscape
Principle: dispersal critical to population size
1. the numbers of an individual are determined by the number of habitable sites and the speed with which they are discovered and colonized
2. discovery depends on the spatial distribution of habitable areas and on the dispersibility of seeds
-time in succession of community; this linked to time factor
-environment: winter inhibition, dry inhibition
When does dispersal start and when does it end?
-How do you differentiate between dispersal and post-dispersal?
-Separate processes of dispersal and post-dispersal largely overlap
-germination or death ends
-abscission potentially very start
-vivipary may be ultimate shortest dispersal interval
What are the separate events of dispersal and post-dispersal?
1. Dispersal is from leaving parent to establishment is all dispersal
a. dispersal from parent plant;
b. post-dispersal movement such as tillage, cropping practices
c. enter soil seed bank then move to new site later
2. Different events overlap, called dispersal and post-dispersal by some
3. ex.: purple loosestrife:
a. disperses from parent plant and falls to bottom of water (disperse event 1);
b. when it germinates it floats to establishment site (semi-dispersal event 2)
4. ex.: galinsoga:
a. starts germination on parent plant (pre-abscission, vivipary; dispersal-establishment event 1);
b. falls to ground already begun germination (head start; dispersal-establishment event 2)
What determines how many seeds are found at a particular site?
What determines the potential population at a site?
Seed flux and population dynamics of a site:
1. Flux of seed into, and out of, a locality determines the potential population at that site;
-inoculum present in an area is the resultant of this flux
-number already there
-# that come in: dispersal
-# that leave, go out: die, dispersal
2. Population dynamics concerned with parameters of this flux:
-gain into site by dispersal
-loss from site by dispersal
-replacement and rearrangement by dispersal within site
3. Flux out for gravity weeds may not be quantitatively significant
4. Flux out for long distance dispersal mechanism possessing plants may be quantitatively important
5. Anecdote: Cocklebur dispersal evolution:
a. evolved along river banks with two dispersal mechanisms:
-barbed burrs to snag macrofaunal vector
-ability to float to move down river to snag site
b. now appears in crop field where floating (or barb) dispersal may be less-not important
c. predict energy invested in dispersal mechanisms be reduced, less barbs-float if evolve in fields
d. evidence of this in Mississippi report of 5 seed capsule: more numbers of seeds (vs. size) for many microsites available in small area of crop fields
What are the two ways, contexts, to look at dispersal?
Dispersal: 2 contexts: parts of the same system: 2 dimensions of colonization
1. expanding range and increasing population size of an invading species into a new area
2. part of the process by which an established and stabilized population maintains itself
3. these are 2 parts of the same intertwined, inseparable, whole: Red Queen analogy: move forward into new areas or lose what area you already occupy
When does evolution favor the development of dispersal structures and mechanisms (5 th seed role, tradeoffs with other seed roles)?
1. Evolution favors development of dispersal structures and mechanisms when there is a greater chance of colonizing a site more favorable than the one that is presently inhabited
2. Ex. of obligate long distance dispersers: mullein, musk thistle
In what 4 dimensions are seed dispersed?
Dispersal in 4 dimensions:
1. distance [horizontal]
2. width [horizontal]
3. soil depth and air height [vertical]
Anecdote on dispersal:
My experience in Czech republic along Elbe and grain traffic from US in the cold war years. How pigweed in grain crops from the US was seen as a capitalist imperialist plot to disperse weed seeds. Irony of Old World invader re-invading the Old World. "What goes around, comes around"
In what two (or more?) ways are seed dispersed in time?
1. in time (dormancy):
-dispersal and dormancy are overlapping strategic options; trade-offs?
-dispersal: escape to somewhere else
-dormancy: wait until the right habitat re-appears
2. in time (shattering) (physiological maturity on parent plant, abscission):
-fall with crop, human movement
-before harvest: escape seed cleaning death
3. in time, over years: mast years for perennials (e.g. oaks and acorns) when seed produced can vary quite a bit between years; grapes too
4. seed dispersal results in very uneven distribution
What are the 6 categories (processes) of dispersal?
 Wind, air
 Other types (misc.)
What weed species have no specialized dispersal structures or mechanisms? Why?
What is the most typical mechanism of dispersal among weed species?
Why is gravity the best?
1. Most seed of our common crop field weed species have no specialized structures and mechanism:
-purple loosestrife (mechanism #1 of several)
2. most seed dispersal acts to leave seed at base of parent, decreasing numbers with distance; move as a horizon, front
3. Weeds that favor their present site, no dispersal structures, mechanisms
4. allows seed to fall in cracks in soil, plant self
What cost do specialized dispersal structures or mechanisms have for a species? Why?
1. Dispersibility has a cost to the plant, but not always
2. specialized structures cost at expense of embryo or food reserves
3. cost of these structures is a measure of fitness advantage to ancestors who have gained by placing descendants at a distance, rather than close by, parent
4. some dispersal comes at no apparent cost to the plant: dust, human movement
5. weeds usually have no specialized structures for dispersal, not worth cost
6. later succession plants (even weeds like milkweed, thistles) do invest in distant dispersal mechanisms/structures because they are often in competition with parents at that site
What are the four different morphological adaptations, structures for wind dispersal (Hint: 3 involve energy cost by plant, one for free)
-dispersal for free; involved with trade-offs mentioned in last chapter
-so light can stay up even in still air
-poppies, fungal spores, ferns, parasitic plants, orchids
-see discussion from last chapter on very small seed size
-can dissolve in water, rain drop, and disperse that way
2. plumes and pappuses
-a feather, or feather-like structure
-a circle or tuft of bristles, hairs, or feathery processes (could be plume-like) in place of a calyx
-typical of Compositae family:dandelion, milkweed, sowthistles
3. wings with concentrated central mass:
-adapted to still air, lift and distance
-stable flight, glide
-ex. lianes (woody vines) and tropical forest trees
4. winged seeds and fruits which rotate when they fall
-symetrical and asymetrical affect where fall
-ex. maple seeds
What different adaptations in weeds produce the same wind dispersal effects?
5. Evolutionary pathways producing the same wind dispersal effect:
-increase ratio of pappus to achene
-improve the drag efficiency of the pappus
-release the seed from higher
6. Soil surface roughness affects wind blown distance
7. accumulate along fence rows, along furrows: traps
8. Movement of the parent plant with seeds:
-velvetleaf capsules and branches (my story about Michigan farmer, top of plant blowing over snow into neighbors yard)
-a tornado can move any seed
9. Isolated plants differ: plants that don’t leave their seed nearby, dispersed widely:
-characteristic of plants in isolation;
-mullein, musk thistle in pasture
10. Specialized wind dispersal mechanisms, structures: don’t colonize and move as a front or horizon, but as isolated individuals over a greater distance
What are the 4 different ways water disperses seed?
-low specific gravity seed; milkweed;
-flattened seed shape,
-ex. corky seed wings, curled dock seed
-concentrate on edges of water, best establishment site?
-ex. cocklebur; waterhemps?
-ex. coconut float in ocean; long distance movement of heavy seed with low specific gravity
#2. movement with surface water, irrigation, rivers, lakes
#3. flooding has big influence, long distance movement
#4. move over soil surface with surface water (erosion):
-stir and mix seed in soil for germination, affects seed banks, shift distribution of seed
-slippery seed move easily over soil surface
Example.: mangrove at mouth of river; propagule is a stick that floats upright; held at right height to germinate when it comes against lands edge; seed at bottom of stick at right location to germinate by shore; breathing roots
#4 Animal, Non-Human
What are the 3 different ways animals disperse seed?
#1. Eating, digestability and viability: [chemical and physical actions]
a. cuts several different ways:
-eat and disperse;
-eat and destroy;
– eat and remove dormancy factor (e.g. physical scarification by gut action, acids, abrasion, etc. of hard seed coat dormancy type species)
-when seed dispersed with animal feces, feces provide nutrients, microsite qualities
b. attractive to animal eating: specialized structures at energy cost; e.g. pollenation
c. species specific feeding patterns affect seed dispersal
d. pass through gut with viability intact
e. gizzard or gut can kill, scarify, remove dormancy
f. remove dormancy;
g. eat fruit, pass on seed, leave with manure pile (nutrients, dormancy?)
h. migratory birds (ducks, geese) can vector long distance dispersal
i. bird roosting sites: red cedar trees in Okla.: along fence lines, birds sit on fence and defecate out seeds, germinate there, protected
j. animals can break open fruit and expose seeds for dispersal without eating seeds
k. plants with attractants, fruits, flowers that draw animals to them to then disperse seed; ex. trilium with eliasomes: ants eat oil body structure with seed attached after collecting
#2. Animal storage:
a. distance, concentration, location
b. ant, cache seed in nest; when germinate they move them out, zone of germination outside of nest
c. mouse cache,
d. manure pile to more favorable germination site
#3. Specialized movement structures:
a. burrs: cocklebur, sandbur
b. spines (no movement),
c. barbs, hooks: foxtail barley, beggarticks
d. seed-mud-fur: glue, sticking to animal
These 3 lead to special pattern: Animal vectors: spatial distribution patterns related to how they move seed
a. long distance are dispersed farther apart
b. short distance (e.g. gravity) close together
c. animals can cause clumping: storage site, defecation site (e.g. under a fence row)
What are the different ways humans disperse seeds?
1. All of the above for non-human animals applies to humans
2. Local dispersal:
-with equipment (cultivators, tillage, combines, planters); carried along this way with mud, grain or feed on equipment too
-feed, seed as contaminants
-attach to humans: burrs, barbs, etc.
3. Long distance dispersal: in things moved around the world
-ship ballast, soil and seed
-crop seed, grain sales
-campers in wilderness areas; waffle-tread hiking boots pick up easily
4. Imported crops that turn to weeds once introduced:
-opuntia cactus in Australia as border plant
-kudzu as forage
-johnsongrass as forage
-hemp, velvetleaf as fiber crops
-multiflora rose as border, hedge
-Plantana cantaria: hedge introduced in Kenya, now weed
-ground ivy: cover crop introduced now weed
-butter & eggs, Linaria spp.:
-honeysuckle in woods as weed
-purple loosestrife: horticultural crop
5. crop with weed seed in it:
-poor combine separation, poor sieving
-soybeans with nightshade seed stuck to it, bin beans
-weed seed in hay as moved
-commercial seed with weeds in it
6. Crop mimicry:
-looks like crop, moved with crop seed: barnyardgrass in rice
-same size, shape as crop seed: nightshade berries in dry beans
-herbicide resistant weeds (in broadest sense of dispersal, we create means of dispersal)
7. Become a crop, or a plant that humans like: crops, medicines, ornamentals, drugs, . what others?
#6 Other structures, mechanisms:
1. seed ejaculation:
-mistletoe and other parasitic weeds,
-water potential differences (ex.’s?),
-explosion (propulsion, click) (ex’s?);
-milkweed capsule cracks and seeds with pappus partially ejected because seeds highly compressed in capsule
2. sticky seed:
-stick to bird feet on plant branch
-nightshade berry breaks in combine with soybeans, sticky juice dries and sticks seed to crop seed
-rugose, rough seed sticks to mud easier than smooth seed
-other interactions of seed surface and soil roughness; seed aggregation traps
3. hygroscopic awns: self-planting by twisting of awns (Avena fatua; Erodium spp.)
4. pappus, plume holds seed in soil crack, keep it near the surface, proper planting depth, shallow (dual role with wind dispersal)
5. chaff: bluestem glumes around seed hold it in cracks, openings in good germination position
1. The numbers of an individual are determined by the number of habitable sites and the speed with which they are discovered and colonized
2. Discovery depends on the spatial distribution of habitable areas and on the dispersibility of seeds
3. Dispersal critical to population size
4. Most seed dispersal acts to leave seed at base of parent, decreasing numbers with distance
5. Isolated plants differ: they are dispersed widely
6. Dispersibility has a cost to the plant:
a. specialized structures not for embryo or food reserves
b. cost of these structures is a measure of fitness advantage to ancestors who have gained by placing descendants at a distance, rather than close by, parent
Ipomoea triloba, Littlebell
Ipomoea triloba L., Littlebell, Aiea Morning Glory
Convolvulaceae, the Morning Glory Family
Littlebell is a vine with a twining or creeping habit. It is not a high climber but is more often seen scrambling through grasses and over low shrubs. Stems rarely exceed 10 feet. When cut, the stems and the petioles (leaf stalks) exude a small amount of milky sap. The leaves are variable in size (ranging from ¾ to 3 ¼ inches long) and in outline (heart-shaped, three-lobed or five-lobed). Flowers are borne in the leaf axils; they are sometimes solitary but more often in small clusters. The pink to pale purple flowers measure ½ to 1 inch long and are funnelform (gradually widening from base to apex) with five short lobes, each ending in a short, abrupt point. The sepals are in two unequal whorls (the outer two shorter than the inner three), oblong in shape, with minutely ciliate margins and ending in a distinct, abrupt point. The fruit are small (about ¼ inch wide), globose capsules with a persistent style. Each capsule contains two to four dark brown seeds.
This species is native to the West Indies, Mexico, Belize and Trinidad, but it is now widely naturalized throughout the tropics.
Occurrence in Florida
The first record of littlebell in Florida is from Monroe County in 1891. By the 1980s, it was recognized as a serious weed of citrus groves, especially in Hendry County. Littlebell has now been documented from many Florida counties, including the entire southern peninsula, parts of the central and northern peninsula, and the central panhandle. It is typically found on disturbed sites such residential landscapes, nurseries, abandoned homesites, agricultural fields, orchards, old pastures and highway and utility corridors.
Similar Species in Florida
Littlebell is most likely to be confused with tievine (Ipomoea cordatotriloba, previously known as Ipomoea trichocarpa), a native species that is frequently found on disturbed sites throughout Florida. It is also very similar to the cultivated sweet potato, Ipomoea batatas. However, both of those species have flowers 1 ¼ to 3 inches long, while the flowers of littlebell are always less than an inch long. Whitestar (Ipomoea lacunosa) is a native morning glory with a low, scrambling habit and flowers as small as those of littlebell, but its flowers are white with purple anthers (littlebell flowers are pink or purple with white anthers). Ivyleaf morning glory (Ipomoea hederacea) is a nonnative weedy species with small pink to purple flowers, but it can be distinguished by its sepals. They have very narrow elongated green tips that are even longer than the basal portion.
Means of Dispersal
There is little specific information on the dispersal of this species. In general, morning glory seeds are dispersed by gravity, wind or rain. Some species are dispersed by ground-dwelling birds, turtles or other small vertebrates. Seeds may also be dispersed as contaminants in mechanically harvested grains. Littlebell is occasionally cultivated and may escape from cultivation.
Many references describe this species as an annual (flowering, fruiting and dying within one year), but in fire-prone habitats in Australia it has behaved as a perennial, developing a lignified tuber over time.