Elana Benamy's whole life is arranged around noticing the little things.

It starts each workday when the curatorial assistant at the Academy of Natural Sciences climbs onto the Chestnut Hill West. All the way into Center City, she makes sure to notice the paulownias growing beside the tracks, incredible sprays of purple flowers. The trees of heaven, immortalized in the classic novel A Tree Grows in Brooklyn, that sprout from cracks in the sidewalk. The azaleas and rhododendrons in their summer grandeur, planted in people's backyards, visible only to their owners — and to Benamy and her fellow travelers.

She likes to be surprised.

Most mornings, she will press play on her ancient iPod, and to the strains of classical music, Celtic lilts, or jazz riffs, she will begin her work. There's a reason she stares at the flora from the train: For the last two years, flowers have been her entire focus. Benamy, 61, has worked at the academy for 35 years. First, she cataloged fossils, insects, and mollusks. And now, she works with the museum's collection of 1.5 million plant specimens — some dating to the Lewis and Clark expedition, some even older.

Her job is to "digitize" over 300,000 of them, compiling an online catalog funded by the National Science Foundation. As it turns out, there's a lot you can learn from dried, flaking, 200-year-old plant samples — about the diversity of our city's ecosystem, how it's changed as the city has grown, and about how climate change has altered so much of our life, down to the days of the year when flowers bloom.

Even as she takes pleasure in the beauty of the giant ragweed of 1859 from West Philly, the little ferns from 13th and Chestnut dating to 1887 — even if their blooms long ago lost their color — she waits for a surprise.

"Sometimes it's the same, and the same, and the same, and then pow! You come across something really cool," she told me, in her whispering voice, as if to not disturb the flowers.

Last month, she got one.

It was a green comet milkweed, an unassuming plant if ever there was one. The faded cursive label below it read:

"Battlefield of Gettysburg, August 20, 1863."

That surprised her.

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She wondered: What was a botanist doing wandering a battlefield not seven weeks after thousands of men had perished there? Some soldiers were buried in shallow graves on the battlefield itself, their boots literally pushing up out of the daisies. What could compel someone to be out there collecting plants?

Benamy reached out to Richard McCourt, the academy's botany curator, who shared her befuddlement, and to Joel Fry, who curates the historic Bartram's Gardens. The mystery of the Gettysburg milkweed began to unfold.

The man who plucked the plant was Thomas Meehan, a renowned Philadelphian botanist, who would later become the academy's president. His brother Joseph, a plant man himself, was a Union soldier held prisoner at the battlefield there. He would later write a book about the flora of Gettysburg. But that's where the botanists' detective work has so far ended.

Was Thomas there to see a bit of history? Was his brother giving him a tour? Did Joseph, imprisoned on the battlefield, spot a few sturdy milkweeds among the carnage and invite Thomas to come take a gander? Or maybe this was just what plant men did in wartime.

On Thursday, Benamy opened the folder where Thomas's milkweed was kept, dried and pressed. The green sprouts that the monarch butterflies fed on, and soldiers stepped over en route to their fates, had long yellowed.

"A witness to all that carnage," she said.

Albeit a silent one.

She still doesn't know why her 19th-century counterpart took to the battlefield. But she almost likes it best that way.

That way, there still could be a surprise, an answer, waiting for her among the dead flowers.