Knapweeds (Centaurea sp.)

 

Note: these are my notes, they may well be incorrect. Knapweeds are best identified from a side-view of the flowerhead, which shows clear details of the phyllary bracts (green or brown overlapping "scales" at the base of the "flower") Most common in central NJ (my area) is C. nigrescens, Tyrol knapweed. Each bract has a larger green triangle at the base, with a smaller, dark (black or brown) roundish disk on the end, which is fringed with 5-8 bristles on each side. The green triangle never has bristles outside of the disk. The disc does not obscure your view of other bracts.  

 Most common in NJ as a whole (and especially in the coastal plains) is C. stoebe, spotted knapweed. Each bract is triangular shaped with length-wise stripes and a dark border on the upper third. This dark border has bristles. Also, the basal leaves are very divided, moreso than in other Centaurea species.

   

 I don't have a photo of it, but batchelor's buttons, C. cyanus supposedly is a common escape in NJ. It has bright blue flowers with very broad ray flowers, a very different color from any other of the knapweed species. 

 Brown knapweed, C. jacea has larger flowerheads than either Tyrol or spotted knapweed. It's bracts are brown and papery, not triangular-shaped. They can be somewhat bristly at the base of the phyllary, but near the "flower" they are not and are often notched. They are not green, not striped, and not narrow.  

 Black knapweed, C. nigra, is not often seen in NJ. It's bracts seem to be all fringe. They are very narrowly triangular and obscure the bases of the other bracts. They have more than 8 bristles on a side.  

 There is a hybrid of brown and black knapweed, Monckton's knapweed, C. moncktonia. It has strongly fringed lower bracts and papery, notched upper bracts. I believe this is it here:  

 Finally, there is the garden flower, perennial coneflower, C. montana. It has blue ray flowers that are extremely narrow and widely spaced. I don't believe it escapes:

Burdocks (Arctium minus vs. A. lappa)

 A. minus has hollow leaf stems and acute (pointed) leaf tips. 

A. lappa has solid leaf stems and rounded leaf tips.

A. minus has flowers/fruit with short stems, and overall in a cluster following the main stem. 

A. lappa has flowers/fruit with long stems, and overall in a flat-topped cluster. 

A. lappa fruit are larger. 

Guide to NJ asters (Symphyotrichum sp. Eurybia sp. Erigeron sp., Doellingera sp. Oclemena sp.)

This guide is NOT for the Pine Barrens or "down the shore"; there are many species there that are left out here. 

Also, make sure you are not dealing with planted "asters", there are tons more of those as well. 

In central and northern NJ there are five genera with "aster" like flowers: 

Symphyotrichum (the American asters)

Erigeron (the fleabanes)

Eurybia (the wood asters)

Doellingera (the flat-topped asters)

Oclemena (whorled wood aster)

Fleabanes (Erigeron sp.) are the only of the "aster-like" flowers that bloom before August. They have over 50 white or purple rays that are narrower than asters', almost hair-like. They have yellow disc flowers where it is essentially impossible to see individual flowers, they look like a yellow "button". Some will still be raggedly blooming in fall. They have very long, narrow, mostly leafless stems. 

-Philadelphia fleabane (E. philadelphicus): clasping leaves

-Annual fleabane (E. annuus): stems with hair that sticks straight out

-Daisy fleabane (E. strigosus): stems with appressed hair

-Robin's plantain (E. pulchellus): usually basal leaves, longer rays, usually purple, less common

(note that horseweed (E. canadensis) is also in this genus but looks nothing like an aster)

Flat-topped aster (Doellingera umbellata) is not common in NJ. As its name implies, its flowers are in very flat clusters at the top of a very straight plant. It can have several separate clusters or only the one. The rays are white and there are 7-14 (so, not many) rays per flowerhead. The leaves are very uniform, long oval, tapered at both ends, about 2 inches (or a bit less) long. The stems are zig-zag-y and usually reddish-brown. 

-Cornel-leaved whitetop (D. infirma) is also recorded from northern NJ but is very rare. It has taller flowerheads (the green bracts below are taller)

Whorled wood aster (Oclemena acuminata) has large, oval (or long oval) leaves that look whorled if you look down on the flower from above,  and very few flowers with long skinny white rays. It is not common and mostly found in north Jersey woods. 

Wood asters: (Eurybia sp.) have heart-shaped leaves always present on the lower part of the plant and rays generally over 1/2 inch long. They can be white (common) or purplish (rare). The leaves never have winged stems, they are always corsely toothed. The flowers never have more than 20 rays. The flowers are in losely flat-topped clusters (but the leaves are totally different from flat-topped aster) Note that two American asters (Symphyotrichum sp.) also have heart-shaped leaves always present (S. cordifolium and S. lowrieanum), but both have purplish rays under 1/2 inch. 

-White wood aster (E. divericata): common. 5-10 white rays. 5-15 teeth on each side of leaf. V-shaped leaf notches. No glandular hairs on leaves.

-Large-leaved wood aster (E. macrophyla):  not common. 8-20 purple-tinged rays. Glandular hairs all over leaves. 

-Schreiber's wood aster (E. schreiberi): uncommon (but should be present): 6-12 white rays. 15-30 teeth on each side of leaf. Squared off leaf notches. No glandular hairs on leaves. The phyllary (green part below flowerhead) is very tall and narrow. 

American Asters (Symphyotrichum sp. ) are the toughest ones. 

First off, the easy one:

-New England Aster (S. novae-angliae): Big flowerheads. Over 50 rays. Usually dark purple, can be white or pink. Stem very hairy, leaves clearly clasp the stem. Generally any non-planted large aster with over 50 rays in northern NJ is this species. 

Note that there are several rarer species of aster with large flowerheads (1 inch across, roughly) and purple flowers that I am not covering in this guide. None have over 50 rays.

The ones with heart-shaped leaves always present:

-Common blue aster (S. cordifolium): unwinged leaf stalk, heart shaped lower leaves, under 20 short, purple-ish rays. 

-Lowrie's aster (S. lowrieanum): winged leaf stalk, heart-shaped lower leaves, under 20 short, purple-ish rays. 

If you find one with large-ish, non-linear,  leaves present and no heart shaped leaves at the base of the plant, leaves have teeth, flowers small, few white rays it is probably Calico aster (S. lateriflorum)

Finally, the beastly ones. All often drop their main leaves, all have small white flowers, all at least sometimes have small linear leaves by the flowers. For all of these see my separate entry just on small white asters. 

-Panicled (or common white) aster (S. lanceolatum)

-Calico aster (S. lateriflorum)

-Frost (or hairy white oldfield) aster (S. pilosum)

-Small white aster (S. racemosum)

-Heath aster (S. ericoides) should be west of here but may be present

And a very uncommon, but possibly present species that looks like these but with small blue/purple flowers is probably bushy aster (Symphyotrichum dumosum).

Another aster-like species is Ionactis linarifolia, like a smallish purple aster with short straight grass-like leaves and no branching. 

Guide to small white asters (Symphyotrichum sp.)

 Here is my working guide to white asters (Symphyotrichum sp.)(without heart-shaped leaves) in central and Northern New Jersey. Note that all of these can have purple flowers as well, though uncommonly.

The phyllary bracts are extremely important (the green bits below the "flower") 

Heath aster  is the only one with pointy, all-green, divergent bracts

Calico aster is the only one with very wide-spread, even curved-back disc flowers

Frost aster is the only one with sort of urn-shaped phyllaries and the only one with green, needle-shaped, spreading bracts that curve away from the stem

Small white and panicled asters both have green striped bracts (calico has green-tipped, spotted looking bracts). 

The number of rays and the size of the rays are important. Heath and calico have smaller flowers with few rays. Small white has small flowers with many rays.

The overall shape of the flower cluster is important. Is it widely branching? (if not, then not heath or small white). Is it one-sided (if not, then not small white).

Leaves are generally unimportant, but only calico and panicled can have leaves that are not linear.

	S. ericoides	S. lateriflora	S. pilosum	S. racemosum	S. lanceolatum
	heath	calico	frost	Sm white	panicled
rays	8-20	9-14	16-35	15-30	20-40
disk		recurved
one-sided?	some		some	usually
branching	Divergent recurved	Widely branch Or simple	Oft. diffuse	Open  Divergent Oft. racemous	elongate
leaves		Sometimes not  linear
Leaf bases				Sometimes clasp	Sometimes petiole-like
Leaf max. (cm)	6 x 0.7	15 x 3	10 x 1	11 x 1	15 x 3
involucre			Constricted (urn-shaped)
bracts	loose		Loose
tips of bracts	With sharp point	Fairly broad green tip	Inrolled margins	Elongate green tip	Elongate green tip
Rays clearly longer than green base (involucre)	no	no	probably	yes, though flowers are small.	yes
location	dry	dry		Moist	moist

S. dumosum, though not common according to iNaturalist in NJ, should also be present. It would have long, bracty stems on flowerheads, bracts green and appressed, 12-20 not terribly long rays, smallish linear leaves. 

Guide to Bidens sp. (Beggar ticks, Tickseed-Sunflower, etc.)

Bidens are fall wildflowers, some are restricted to wet areas, some are not.

There are two simple to separate from the others:

-Spanish Needles (B. bipartita) has leaves twice compound. 

-Beck's Water Marigold (B. beckii) is very rare, grows actually in water, and has underwater leaves that are hairlike and whorled. 

That leaves four groups of species, separated by have rays/lack rays and simple leaves/ once divide leaves.

Ray flowers present, and once divided leaves: Tickseed-Sunflowers:

-Tickseed-Sunflower (B. aristosa) 8-12 somewhat curled large green bracts below flower

-Marsh Tickseed-sunflower (B. trichosperma) 8-12 flat, broad green bracts below flower; long, skinny fruit

-Long-Bracted Tickseed Sunflower (B. polylepsis) 12-20 curled, long green bracts below flower

-White Beggarticks (B. alba): white rays (rare if present at all in NJ)

Ray flowers present, undivided leaves: Bur-Marigolds:

-Bur-Marigold (B. laevis): large rays, just like the tickseed sunflowers but note undivided leaves

-Nodding Bur-Marigold (B. cernua): short rays (1 in?) sometimes none, plant short (8 in?) on edge of water, always nodding. Sessile leaves.

No ray flowers, divided leaves: Beggarticks: 

-Devil's beggarticks (B. frondosa): 5-10 large green bracts below flowerhead (extremely common)

-Tall Beggarticks (B. discoidea): 3-5 large green bracts below flowerhead

-Swamp Beggarticks (B. vulgata): 10-20 large green bracts below flowerhead 

No ray flowers, undivided leaves: Beggarticks (and Bur-Marigold)

-Beggarticks (B. connata): long, unwinged stem on leaf.

-Three-Pronged Beggarticks (B. tripartita): short, winged stem on leaf

-Nodding Bur-Marigold (B. cernua) when it lacks rays looks like these. Leaves have no stem.

Late Boneset (Eupatorium serotinum)

Nodding Beggarticks (Bidens cernua)

Common Sow-Thistle (Sonchus oleraceus)

Prickly Lettuce (Lactuca serriola)

Canada Wild Lettuce (Lactuca canadensis)

Tall Blue Lettuce (Lactuca biennis)

Clotbur / Rough Cocklebur (Xanthium strumarium)

Bristle Thistle (Cirsium horridulum)

Mugwort (Artemisia vulgaris)

fruit brown, chaffy, but not obviously fluffy, purple fall/early winter leaves white below

lobed leaves, generally with a winged stem and fairly sharp points

flowering spike generally with unlobed leaves

stem is very hairy

young leaves with lobes more rounded, still pointed at tips, stem winged at least near lobes

fruiting stalk lasts all winter

fall color reddish, turns early 

late fall/ winter leaves dark gray, curled, with light underside showing

flowers

light underside to leaves

leaves white below

flowers often look almost white with red-brown tips, not one-sided (as in ragweed)