Acanthaceae (PDF file)

Acanthaceae 

Acanthus Family

Introduction 

• Perennial herbs, vines 

or occasionally shrubs 

• Sometimes armed

Leaves 

• Simple 

• Usually entire 

• Oppositely arranged 

(decussate) 

• Exstipulate (no stipules)

Inflorescence 

• Determinate 

(inflorescence in which 

the terminal or central 

flower opens first) 

– Cymose 

– Often appearing 

racemose, paniculate, or 

spicate 

• Flower sometimes 

solitary

Flowers 

• Zygomorphic 

(bilaterally symmetrical) 

• Perfect 

• Hypogenous (superior 

ovary) 

• Showy 

• With nectariferous disc 

• Often subtended by 

conspicuous bracts

Calyx 

• Synsepalous (sepals 

fused together)with 5 

or sometimes 4 lobes 

• Convolute (overlapping) 

or imbricate 

(overlapping like 

shingles) 

• Persistent

Corolla 

• Sympetalous with 5 

lobes 

• Usually bilabiate 

(having 2 lips) 

• Imbricate or convolute 

• Variously colored

• Usually 4 stamens 

• Didynamous 

– If didynamous then 1 

staminode present 

• Sometimes reduced to 

2 stamens and 2 

staminodes 

• Epipetalous 

• Filaments distinct or 

coherent in pairs 

Androecium

• Anthers more or less 

basifixed 

• 2- or 1-locular 

– Locules unequal and at 

different levels 

• Sometimes spurred 

and/or hairy 

• Sometimes with 

prominent connective 

• Dehiscing longitudinally 

Androecium

• Of 1 pistil 

– 2-carpellate 

• Superior ovary 

– 2-locular 

• 1 style 

– Slender 

– Filiform 

• Stigmas 1-2 

– Funnelform or 2-lobed 

– Often with a reduced 

posterior lobe 

Gynoecium

Gynoecium 

• Ovules 2-10 in 2 rows in 

each locule with 

modified funicle 

• Placentation axile

Fruit 

• An elastic loculicidal 

capsule 

– With 2 recurving valves 

• Seeds usually flat 

– Supported by small 

hook-like projections 

• Retinacula 

• Jaculators

Fruit 

• With very thin, 

mucilaginous (slimy) 

seed coat 

• Endosperm usually 

absent 

• Embryo large 

– Curved, bent, sometimes 

straight

Representative 

Genera

Anisacanthus quadrifidus var. wrightii 

• Small, bushy shrub 61-122 cm 

tall 

• Soft hairs line the stems from 

between one pair of leaves to 

the axils of the next lower leaf 

pair 

• Lanceolate leaves up to 5.7 cm 

long, with petiole; hairs line the 

midrib and petiole 

• Orange flowers about 3.8 cm 

long and in terminal spikes 

Flame acanthus

Dyschoriste linearis 

Snake herb 

• Rather stiffly upright, coarsely and 

stiffly hairy perennial, 18-30 cm tall; 

stems 4-angled, few to several, 

usually unbranched 

• Leaves 16-50 mm long, opposite, 

stalkless, rather rigid; margins fringed 

with hairs 

• Flowers 16-35 mm long, bluishpurple 

or lavender, dark-spotted in 

throat, hairy outside, somewhat 

tubular, 2-lipped; upper lip unlobed; 

lower lip deeply 3-lobed; stalkless, 

from upper leaf axils

Justicia americana 

American water-willow 

• Upright, smooth perennial herb to 76 cm; 

stems angled, slender, branched in upper 

portion, usually rooting in lower portion 

• Leaves 7.6-15 cm long, narrow, opposite, 

stalkless or almost so, narrowed at both 

ends; margins entire 

• Flowers 10-13 mm long, white or 

occasionally violet, dotted with purple, 2- 

lipped; upper lip notched or 2-lobed, 

turned backward; lower lip deeply 3- 

lobed, occasionally turned under; flowers 

few, in cluster at tip of long stalk from 

leaf axils

Ruellia drummondiana 

• Coarse erect plant, 30-91 

cm tall; stem 4-angled 

covered with short, stiff, 

slightly rough hairs 

• Leaves 5-15 cm long with 

undulating margins; on 

petioles 1.3-2.5 cm long; 

usually dark green on the 

upper surface and pale 

green on the lower surface 

• Cluster of 2-7 flowers grow 

from leaf axils; purple to 

light purple; 3.8 cm long 

Drummond's ruellia

Ruellia humilis 

Fringeleaf wild petunia 

• Upright to somewhat sprawling, clumped, 

rather stout, conspicuously hairy perennial up 

to 81 cm tall; stems usually several in a clump, 

prominently 4-angled, branched; branches 

slender often lying on the ground 

• Leaves to 8 cm long, 4.5 cm wide, opposite, 

essentially stalkless, somewhat crowded on 

the stem; blade leathery, blunt or wedgeshaped 

at base and extending onto stalk, blunt 

or sharp-pointed at tip, densely hairy on veins 

and margins 

• Flowers 5-8 cm long to 2 cm wide, lavender to 

purplish-blue, usually with darker markings in 

the throat, trumpet-shaped, deeply 5-lobed at 

the rim; flowers few in clusters from middle 

and upper leaf axils

Ruellia nudiflora 

Violet ruellia 

• Upright to semi-sprawling perennial to 

71 cm tall from a somewhat woody 

base; stem solitary, branching in upper 

portion; plant densely hairy when young 

becoming almost entirely smooth with 

age 

• Leaves generally 6 cm long and 3 cm 

wide, opposite, stalked; blade graygreen, 

prominently net-veined on lower 

surface; margins curled or wavy-toothed 

• Flowers 55 mm long, 38 mm wide, 

lavender to purple, trumpet-shaped, 

deeply 5-lobed at rim, conspicuously 

curved, falling from plant in early 

afternoon

• Duration: Perennial 

Habit: Herb 

Leaf Complexity: Simple 

Leaf Shape: Ovate 

Leaf Venation: Pinnately 

Veined 

Leaf Pubescence: 

Puberulent 

Leaf Margin: Undulate 

Leaf Apex: Rounded 

Leaf Base: Rounded 

Flower Size: 7 cm long 

Sepals: calyx lobes linearattenuate 

Size Class: 1-3 ft. 

Ruellia occidentalis 

Western wild petunia

NEXT 

Solanaceae 

Nightshade 

Family

Acanthaceae (PDF file)

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